Encyclopedia | Hairmetry

1

other

18-MEA (18-methyleicosanoic acid)

The fatty acid on the outer surface of virgin hair that makes it water-repellent and smooth, lost with weathering and chemical treatment.

A

protein or peptide

Acetyl tetrapeptide-3

Acetyl tetrapeptide-3 is a short peptide sold in hair serums, almost always with biochanin A; one small trial of a three-part blend matched 3% minoxidil.
drug with hair side effects

Acitretin

A prescription retinoid for severe psoriasis whose most common side effect is hair thinning, and which must never be used in pregnancy.
styling polymer

Acrylates copolymer

A family of acrylic polymers that thicken styling gels and dry to a hard, clear film for strong hold.
growth stimulant

Adenosine (topical)

Adenosine, a natural signalling molecule, is the cosmetic hair active with the cleanest small placebo-controlled trials, mainly making thin hairs thicker.
protein or peptide

Afamelanotide and melanotan

Skin-tanning peptides discussed online as hair-darkeners, but no study shows any effect on gray hair, and unlicensed melanotan injections have been linked to melanoma in case reports.
protein or peptide

AHK-Cu (copper tripeptide-3)

AHK-Cu is a copper peptide that lengthened human hair follicles in a 2007 lab study but has no human hair-growth trial.
other

Alcohol denat.

Ordinary ethanol made undrinkable, a fast-drying solvent in hair sprays and gels that is not the same as the fatty alcohols in conditioners.
antiandrogen

Alfatradiol

A weakly hormonal topical estradiol approved for pattern hair loss in Germany; in the one randomised comparison it only slowed loss while minoxidil grew hair.
botanical

Aloe vera

Aloe gel is a soothing, water-binding scalp and hair conditioner, with no solid human trial showing it grows hair.
supplement

Alpha-ketoglutarate (and alpha-ketobutyrate)

Two ordinary body metabolites woke dormant mouse hair follicles in a 2019 study, and oral alpha-ketobutyrate prevented hair loss in aged mice, but there is no human data.
other

Aminexil

Aminexil is a minoxidil-like cosmetic sold as an anti-shedding ampoule, with no human trial and a rat study that found it the weakest of the products tested.
protein or peptide

Amino acids

Free amino acids in conditioners are small enough to enter hair, but there is little evidence that they strengthen it.
botanical

Amla

Amla fruit has one small positive placebo-controlled trial of an oral syrup in women with pattern hair loss, plus lab and animal data; amla oils and masks are tradition.
chemical treatment

Ammonia and monoethanolamine (MEA)

The alkaline agents that swell the cuticle so dye and bleach can enter; "ammonia-free" MEA dyes are not gentler.
surfactant

Ammonium laureth sulfate

The ammonium-salt version of SLES, an ethoxylated sulfate cleanser that is gentler than lauryl sulfates and can carry a trace by-product called 1,4-dioxane.
surfactant

Ammonium lauryl sulfate

The ammonium-salt twin of SLS, a strong cleanser with essentially the same cleaning power and irritation profile.
chemical treatment

Ammonium thioglycolate

The classic reducing agent in perms and thio relaxers; it breaks hair's disulfide bonds so the shape can change, with some loss each time.
silicone

Amodimethicone

A dimethicone with positively charged amine groups, so it clings to damaged hair and resists rinsing better than plain dimethicone.
botanical

AnaGain

AnaGain is a pea sprout extract with a small maker-run study and mouse data, plausible and low risk but without an independent controlled trial.
drug with hair side effects

Anticoagulants (heparin, warfarin, DOACs)

Blood thinners that can cause shedding about 3 months after starting, which usually reverses and is never a reason to stop on your own.
drug with hair side effects

Antithyroid drugs (carbimazole, methimazole, propylthiouracil)

Medicines for an overactive thyroid; shedding on them can come from the thyroid disease, an over-treated thyroid, or the drug, which is hard to separate.
oil or butter

Argan oil

A popular finishing oil for shine and anti-frizz, with only small lab studies behind it and no significant evidence for hair quality or growth.
botanical

Ashwagandha

A herbal root that lowers measured stress in short trials, with one small hair study and rare reports of serious liver injury.
oil or butter

Avocado oil

A rich oleic-acid oil common in deep conditioners, with no hair-fibre or clinical hair studies found.

B

botanical

Baicapil

Baicapil is a supplier-branded plant-extract active found in hair serums, with no published human trial behind it.
immunomodulator

Baricitinib

A once-daily pill that was the first drug approved for severe alopecia areata, regrowing hair in about a third of patients while they keep taking it.
oil or butter

Batana oil

Batana oil is a trending Honduran palm-nut oil sold for hair growth, with no peer-reviewed hair study found.
oil or butter

Beeswax

The classic hold-and-grip wax in pomades and braiding waxes; harmless for most people but a documented contact allergen for a minority.
conditioning agent

Behentrimonium chloride

A long-chain, positively charged conditioning ingredient that clings to hair and detangles it, with good lab evidence for smoothing and none for repair.
conditioning agent

Behentrimonium methosulfate

The methosulfate salt of the same C22 conditioning ingredient as behentrimonium chloride, slightly weaker in head-to-head lab testing.
conditioning agent

Behenyl alcohol

The longest common conditioner fatty alcohol, a stiff wax that gives rich, thick conditioners; it has no hair-specific studies.
other

Bentonite

A swelling clay used in clay masks and some matte styling products as an absorbent and thickener; "bentonite washes" are untested for hair.
drug with hair side effects

Beta-blockers

Heart and blood-pressure drugs that rarely cause reversible shedding, based on old case reports only.
botanical

Beta-sitosterol

A plant sterol credited with weak anti-DHT activity, but no hair trial has tested it on its own.
botanical

Bhringraj

Bhringraj is the Ayurvedic "king of hair" herb; extracts speed regrowth in rats and mice, but no human hair trial was found.
antiandrogen

Bicalutamide

A prostate-cancer drug that blocks the androgen receptor and is used off-label by some specialists for women's hair loss, with liver-monitoring and pregnancy rules.
growth stimulant

Bimatoprost

A prostaglandin-like eye medicine that grows longer, thicker, darker eyelashes (and helps eyebrows), but did not work on the scalp.
supplement

Biotin

A B vitamin that restores hair only in the rare people who are deficient, and that can scramble thyroid and heart blood tests at the doses sold for hair.
protein or peptide

Biotinoyl tripeptide-1

Biotinoyl tripeptide-1 is biotin attached to the GHK peptide; the only hair-growth data are manufacturer claims.
bond builder

Bis-aminopropyl diglycol dimaleate

The active in Olaplex; it strengthens bleached hair in the lab, but the claim that it re-links broken disulfide bonds has never been independently confirmed.
silicone

Bis-aminopropyl dimethicone

An amino-terminated silicone related to amodimethicone, used in conditioners and colour-care products to stick to damaged hair.
botanical

Black seed oil

Black seed oil's hair reputation rests on animal work and a tiny open-label lotion study, with no independent controlled human trial.
drug with hair side effects

BRAF inhibitors (vemurafenib, dabrafenib)

Melanoma pills that caused hair loss in 2 of 20 patients and curly hair in one in a small prospective study.
drug with hair side effects

Breast cancer endocrine therapy (tamoxifen, aromatase inhibitors)

Anti-estrogen pills taken for years after breast cancer can cause female pattern-type thinning, and in one uncontrolled series topical minoxidil helped 80% of those assessed.

C

growth stimulant

Caffeine (topical)

Caffeine in shampoos and leave-on liquids clearly stimulates hair follicles in the lab, but the human trials are small, mostly industry-run and mostly on blends.
oil or butter

Candelilla wax

A plant wax from a Mexican desert shrub, used as the vegan alternative to beeswax in pomades and balms.
botanical

Cannabinoids and CBD

A hemp-oil case series claims a 93.5% rise in hair count in 35 people, but it had no control group; lab data hint CBD may lift a growth signal in papilla cells while higher doses could push follicles into regression.
protein or peptide

Capixyl

Capixyl is a branded blend of a peptide and a red clover isoflavone; one tiny trial of a similar blend matched 3% minoxidil, with no placebo arm.
supplement

Capsaicin and isoflavone (oral)

One 2007 Japanese study found more hair growth in people taking oral capsaicin plus soy isoflavone than placebo, but it was never replicated, and capsaicin applied directly to follicles in the lab does the opposite.
styling polymer

Carbomer

A cross-linked polyacrylic acid that turns watery formulas into clear gels; in hair gels it is mainly the thickener, not the hold agent.
oil or butter

Castor oil

Castor oil is a thick sealant that suits dry hair, but no controlled human trial shows it grows hair, and in rare cases it has matted a whole head of hair irreversibly.
supplement

Catalase and pseudocatalase

The idea that hair grays because follicles accumulate hydrogen peroxide has a real basis in vitiligo skin, but catalase supplements for gray hair have no human trial evidence.
drug with hair side effects

CDK4/6 inhibitors (palbociclib, ribociclib, abemaciclib)

Breast-cancer pills that cause a thinning pattern similar to androgenetic alopecia, concentrated at the crown, with a slightly weaker response to minoxidil than with hormone therapy alone.
other

Ceramides

Waxy lipids from the cement between hair cells; a lab study with ceramide-containing liposomes restored some lipids and break resistance, but retail products lack hair trials.
conditioning agent

Cetearyl alcohol

A waxy blend of cetyl and stearyl alcohols that thickens conditioners and builds the gel that carries the conditioning agent; despite the name, it is not a drying alcohol.
conditioning agent

Cetrimonium chloride

A shorter-chain conditioning ingredient, a bit less effective than the behentrimonium salts but lighter, found in many shampoos, light conditioners and sprays.
conditioning agent

Cetyl alcohol

A 16-carbon fatty alcohol that thickens conditioners and pairs with conditioning surfactants to form the gel; it is not a drying alcohol.
drug with hair side effects

Chemotherapy hair changes ("chemo curls")

Hair often regrows curlier, softer or a different colour after chemotherapy, but nobody has measured how often; what is better documented is that permanent thin regrowth is more common than once believed.
anti dandruff

Ciclopirox

An antifungal shampoo ingredient with randomized-trial support for scalp seborrheic dermatitis and a particular edge on itch, with no good evidence that it grows hair.
chelator

Citric acid

The most common pH adjuster in shampoos and conditioners and, in a 2025 lab study, a calcium-removing treatment that strengthened chemically treated hair.
antiandrogen

Clascoterone

A topical androgen blocker already approved as an acne cream whose 5% scalp solution reported positive phase 3 results in men; it is not yet approved for hair.
anti dandruff

Climbazole

A cosmetic azole antifungal used mostly as a booster next to zinc pyrithione or piroctone olamine, with thin evidence on its own.
anti dandruff

Coal tar

One of the oldest dandruff and psoriasis treatments; it works, but it contains carcinogens, smells, stains and is no longer anyone's first choice.
surfactant

Cocamide MEA and cocamide DEA

Foam boosters and thickeners in shampoo; the DEA type raises nitrosamine and allergy questions, which is why many brands moved to MEA or other thickeners.
surfactant

Cocamidopropyl betaine

The most common helper surfactant in shampoo, which makes sulfate cleansers gentler, thicker and foamier, and a rare cause of scalp allergy that usually comes from manufacturing impurities.
surfactant

Coco-glucoside

A coconut-derived mild cleanser that is a staple of sulfate-free shampoos, with the same contact-allergy caveat as decyl glucoside.
oil or butter

Coconut oil

The best-studied hair oil; in lab work it cut protein loss and fatigue damage when used before washing, but almost all studies come from coconut-oil sellers.
protein or peptide

Collagen peptides

A protein powder with modest skin evidence and very little for hair.
supplement

Creatine

The idea that creatine causes baldness comes from one 2009 rugby study that never looked at hair; a 2025 randomised trial found no effect on DHT or hair.
silicone

Cyclopentasiloxane

A volatile silicone that spreads easily and evaporates, used to carry heavier silicones in serums; now restricted in the EU for environmental reasons.
immunomodulator

Cyclosporine (ciclosporin)

A transplant and psoriasis immunosuppressant that makes hair grow as a side effect and works off-label in alopecia areata, but is toxic to kidneys and blood pressure.
antiandrogen

Cyproterone acetate

A steroid antiandrogen used in Europe for women's hair loss and excess hair, with mixed trial results and a dose-related risk of meningioma.

D

surfactant

Decyl glucoside

A plant-derived mild cleanser marketed as ultra-gentle, but its best-documented concern is a rising rate of contact allergy.
immunomodulator

Deuruxolitinib

A twice-daily JAK pill approved in the US in 2024 for adults with severe alopecia areata, giving about 3 in 10 people near-full scalp hair at 24 weeks.
growth stimulant

Diazoxide

A potassium-channel-opening drug related to minoxidil that causes heavy fine body hair as a side effect and regrew hair on bald macaques, but has never been tested for human hair loss.
silicone

Dimethicone

The standard hair silicone, a water-insoluble oil that coats the fibre for slip, shine and friction control without repairing anything.
silicone

Dimethiconol

A dimethicone with hydroxyl end groups, usually supplied as a thick gum emulsion for longer-lasting slip in rinse-off conditioners.
pathway modulator

Dipyridamole

An old antiplatelet pill that on paper boosts the same adenosine pathway topical adenosine uses, but no study has ever tested it on hair and its label lists hair loss as a rare report.
chelator

Disodium EDTA

The classic cosmetic chelator, which grabs calcium, magnesium, iron and copper so shampoos lather and keep in hard water, with no clinical hair trials of its own.
surfactant

Disodium laureth sulfosuccinate

A mild anionic cleanser often used as a secondary or co-primary surfactant that helps blends stay gentle while still cleaning.
immunomodulator

Dupilumab

An eczema antibody that halted worsening of alopecia areata in a 40-person phase 2a trial, especially in people with high IgE, although absolute regrowth rates were modest.
antiandrogen

Dutasteride

A stronger cousin of finasteride that blocks both forms of the DHT-making enzyme and grew more hair than finasteride in head-to-head trials.

E

other

Eflornithine

A cream that slows hair growth by blocking the polyamine pathway, improving unwanted female facial hair in trials, with growth returning within 8 weeks of stopping.
drug with hair side effects

EGFR inhibitors (erlotinib, cetuximab)

Cancer drugs that block the EGF receptor can make eyelashes grow abnormally long and curly, and scalp hair curly or brittle, all reversing after the drug stops.
oil or butter

Emu oil

Emu oil is a rendered bird-fat moisturizer with some mouse anti-inflammatory data, marketed for hair growth without any hair trial behind it.

F

botanical

Fenugreek

A seed used in traditional hair oils and masks with no human hair-growth trial behind it.
antiandrogen

Finasteride

A prescription pill (and in some countries a scalp spray) that lowers DHT and is the best-proven drug for stopping male pattern hair loss.
botanical

Flaxseed gel

A homemade or commercial gel of boiled flax seeds, popular as a natural curl definer, with no published study on it as a hair styler.
antiandrogen

Fluridil

A topical antiandrogen designed to break down in the skin; its only human evidence is one small 2002 trial by its inventors.
antiandrogen

Flutamide

An older prostate-cancer antiandrogen that helped women's hair loss modestly in one small trial but carries a boxed warning for liver failure.
supplement

Folate (vitamin B9)

A B vitamin that is sometimes low in people with hair loss, but not a hair-growth supplement if your levels are normal.
chemical treatment

Formaldehyde and formaldehyde releasers (methylene glycol)

The cross-linker behind classic keratin smoothing; it works but releases a human carcinogen when heated, and even "formaldehyde-free" versions can exceed workplace limits.

G

botanical

Garlic

A 2007 Iranian trial found garlic gel added to a steroid cream improved patchy alopecia areata, but raw garlic is a known skin allergen and nothing supports it for pattern hair loss.
protein or peptide

GHK-Cu (copper tripeptide-1)

GHK-Cu is a copper-binding peptide with a long skin-repair record but no published controlled trial for hair growth.
drug with hair side effects

GLP-1 receptor agonists (semaglutide, tirzepatide)

The new weight-loss injections list hair shedding as a side effect in about 3-6% of trial participants versus about 1% on placebo, far more often in women, and it appears tied to weight loss rather than toxicity to follicles.
humectant

Glycerin

A cheap water-binding ingredient in nearly every conditioner; no peer-reviewed hair study tests it, and the popular humidity rules are untested.
chemical treatment

Glyoxylic acid

Marketed as a safe "formaldehyde-free" straightening agent, but it has been linked to acute kidney failure and the EU has begun a safety review.
botanical

Green tea EGCG

EGCG, the main green tea catechin, grew human hair follicles in a dish, but there is no good human trial of it alone for hair loss.
antiandrogen

GT20029

A topical drug that tags the androgen receptor for destruction instead of just blocking it; a 12-week phase 2 in Chinese men showed modest gains.
conditioning agent

Guar hydroxypropyltrimonium chloride

A plant-derived cationic polymer used in conditioning shampoos and "natural" conditioners to ease wet combing; it can build up on hair.

H

supplement

Hair supplement blends (Nutrafol, Viviscal and similar)

Branded multi-ingredient hair vitamins that beat placebo in small, mostly company-linked trials.
drug with hair side effects

Hedgehog pathway inhibitors (vismodegib, sonidegib)

Skin-cancer pills that block the Hedgehog pathway, which drives follicle growth, caused hair loss in 56.9% of patients in a meta-analysis, the highest of any targeted cancer drug.
botanical

Hibiscus

Hibiscus leaf and flower extracts grew hair in rats and cultured rat follicles, but no human hair trial exists.
growth stimulant

HMI-115

An injected antibody that blocks the prolactin receptor, with a small open-label hair gain and an unreported 192-man phase 2 trial in men.
humectant

Honey

A sugar-rich natural humectant used in DIY and commercial masks; no hair-fibre study was found.
humectant

Hyaluronic acid

A large water-binding sugar molecule added to some leave-ins and masks; no hair-fibre study was found.
chemical treatment

Hydrogen peroxide

The oxidiser in every bleach and permanent dye; it lifts colour by destroying melanin but also oxidises the hair's own proteins, so damage rises with strength and repeat use.
protein or peptide

Hydrolyzed keratin

Keratin fragments, usually from wool or feathers, that coat damaged hair and in lab tests partly entered it and raised wet strength; the evidence is small and industry-linked.
protein or peptide

Hydrolyzed rice protein

A plant, gluten-free protein used in conditioners and volumizers; we found no hair study for it.
protein or peptide

Hydrolyzed silk

Silk-derived peptides added for gloss and softness; the cosmetic safety panel judged most silk proteins safe, but there is no hair efficacy study.
protein or peptide

Hydrolyzed wheat protein

A common conditioner protein that raised dry strength of bleached and heat-damaged tresses in one lab test, with a small but real allergy risk.
drug with hair side effects

Hydroxychloroquine

A malaria and lupus drug that is the most-used pill for scarring alopecias such as lichen planopilaris and frontal fibrosing alopecia, with no randomized trial behind it, and whose cousin chloroquine can lighten hair colour.

I

drug with hair side effects

Imatinib

A leukaemia drug that blocks the receptor pigment cells depend on can lighten or whiten hair reversibly, and oddly has also been listed among drugs that darkened gray hair.
drug with hair side effects

Immune checkpoint inhibitors (nivolumab, pembrolizumab)

Anti-PD-1 cancer immunotherapy darkened white hair in 13 of 14 lung cancer patients in one series, and in a single case left a persistent curly-hair look.
supplement

Iron and ferritin

Low iron stores are common in people who shed hair, but no trial has shown that iron pills regrow hair, and nobody agrees on a hair-specific ferritin target.
drug with hair side effects

Isotretinoin

A prescription acne drug that causes shedding in a few percent of users and, far more seriously, severe birth defects.

J

oil or butter

Jojoba oil

A liquid wax often said to mimic scalp sebum; we found no hair-specific efficacy study.

K

bond builder

K18 peptide (sh-Oligopeptide-78)

A short cysteine-rich peptide modelled on hair keratin; inventor lab data look promising, but the one independent test found it acted mostly as a surface coating.
other

Kaolin

A soft white clay used in matte clays, pastes and dry shampoos to soak up oil and give a dry, textured finish.
anti dandruff

Ketoconazole

An antifungal shampoo ingredient that is among the best-proven treatments for dandruff and, with much weaker evidence, a possible add-on for pattern hair loss.
growth stimulant

Kopexil

Kopexil is a minoxidil look-alike sold in cosmetic serums; a 2025 mouse study found it beat minoxidil, but there is no published human trial.

L

supplement

L-cysteine

An amino acid that makes up much of hair keratin, with no controlled hair trial on its own.
supplement

L-lysine

An essential amino acid once paired with iron for women with shedding, with no recent independent trial.
oil or butter

Lanolin

A sheep-wool wax used as an emollient in pomades and conditioners; a weak but real contact allergen whose true allergy rate is probably under-detected.
growth stimulant

Latanoprost

A cheap glaucoma eye drop that lengthens and darkens eyelashes, with only a small pilot trial behind its off-label use on the scalp.
surfactant

Lauryl glucoside

A 12-carbon alkyl glucoside that foams a little better than decyl glucoside and carries the same class contact-allergy profile.
botanical

Lavender oil

Lavender oil thickened skin and increased follicle numbers in mice in 2016; there is no human hair trial, and a debated hormone-disruption concern exists in young children.
drug with hair side effects

Lithium

A mood-stabilising medicine whose label lists hair thinning, with figures ranging from no excess in trials to about 1 in 5 in older surveys.
supplement

Luteolin

A plant flavonoid sold as a supplement slowed hair graying in a mouse model while two similar antioxidants did not, and there is no human data at all.

M

bond builder

Maleic acid

A small, cheap acid with a reactive double bond that is the working part of Olaplex-type bond builders; evidence that it repairs bleached hair comes from patents and spectroscopy, not controlled trials.
supplement

Marine protein supplements (Viviscal, Nourkrin)

Branded fish- and shellfish-extract pills with positive but small, manufacturer-linked trials.
growth stimulant

Melatonin (topical)

Hair follicles make their own melatonin, and a small 2004 trial found a scalp solution raised the share of growing hairs in women, but later studies are uncontrolled and sponsored by the maker.
drug with hair side effects

Metformin

The world's most-used diabetes pill woke sleeping hair follicles in mice and was linked to regrowth in 6 of 12 women with a scarring alopecia, but there is no randomized hair trial and it is not a baldness treatment.
drug with hair side effects

Methotrexate

A weekly immune-suppressing medicine that thins hair in a few percent of users, and is also used off-label for severe alopecia areata.
other

Methyl nicotinate

Methyl nicotinate makes skin flush and tingle by widening small blood vessels, but no controlled trial shows it grows hair.
supplement

Methylsulfonylmethane (MSM)

A sulfur supplement sold for hair growth with no human hair data behind it.
pathway modulator

Midodrine

A blood-pressure pill that gives many people goosebumps and a tingling scalp because it grips the tiny muscle at each hair; related drugs briefly cut shedding during brushing, but midodrine itself has never been tested on hair.
oil or butter

Mineral oil

A cheap, non-penetrating hydrocarbon oil that coats hair for shine and slip but, unlike coconut oil, did not protect against protein loss in lab tests.
growth stimulant

Minoxidil

The most widely used hair-growth treatment, available as a cheap over-the-counter lotion or foam and as a prescription tablet, with a mechanism that is still only partly understood.

N

supplement

NAD+ precursors (NMN, nicotinamide riboside)

The headline anti-ageing supplements have exactly one hair paper, in DHT-treated mice and cells, and no human hair trial.
other

Nanoxidil

Nanoxidil is a marketing name for a cosmetic "minoxidil alternative" with no chemical definition and no peer-reviewed study that could be found.
other

Niacinamide

Niacinamide is a safe, cheap vitamin B3 form found in many hair serums, but no trial shows it grows hair on its own.

O

oil or butter

Olive oil

A traditional hair oil whose only supporting hair data is that its film thinned on hair like coconut oil did, suggesting some absorption.
supplement

Omega-3 fatty acids

Fish-oil fats whose only hair evidence is a branded omega-3/6 plus antioxidant product tested in women.
botanical

Onion juice

A 2002 Iraqi study found crude onion juice regrew hair in patchy alopecia areata, but the control was tap water, the groups were small, and it was not shown for pattern hair loss.
antiandrogen

Oral contraceptives and antiandrogenic progestins

Some birth-control pills lower androgens or block their receptor, but almost no trial shows that any pill regrows scalp hair.
protein or peptide

Oral keratin supplements

Keratin capsules with one small company-linked trial and no sign that swallowed keratin reaches your hair.
protein or peptide

Osteopontin

Hairy moles are hairy because senescent pigment cells release osteopontin, which woke hair stem cells in mice and stimulated human follicles in culture, while a modified fragment of the same protein did the opposite.

P

colorant

p-Phenylenediamine (PPD)

The main dark permanent dye ingredient and one of the commonest hair-dye allergens; it colours well but can cause severe contact dermatitis in sensitised people.
humectant

Panthenol

A small vitamin B5 alcohol that enters the hair cortex and raised break stress in a lab study; the only humectant here with real hair-fibre data.
supplement

Para-aminobenzoic acid (PABA)

A 1950 physician report described gray hair darkening on high-dose PABA, and the idea has survived 75 years on weak evidence.
pathway modulator

PDE5 inhibitors (sildenafil, tadalafil)

Sildenafil raised growth factors in human hair papilla cells and sped up growth in mice, but its only human hair trial, a tiny open study in children with alopecia areata, showed nothing beyond spontaneous regrowth.
silicone

PEG-12 dimethicone

A dimethicone with polyethylene glycol side chains that makes it water-dispersible, so it rinses out more easily than classic silicones.
botanical

Peppermint oil

In a 2014 mouse study 3% peppermint oil grew more hair than 3% minoxidil, but no human trial of peppermint oil for hair has been found.
chemical treatment

Persulfates (ammonium, potassium, sodium persulfate)

The booster salts in powder lighteners; they speed up bleaching and are a documented cause of occupational asthma and contact allergy in hairdressers.
oil or butter

Petrolatum

A refined mineral-oil-and-wax jelly that is the base of many greasy pomades; it seals and adds shine but does not enter the hair.
drug with hair side effects

Phenytoin

The old epilepsy drug phenytoin is the best-documented anticonvulsant for causing excess facial and body hair, along with acne and gum overgrowth.
anti dandruff

Piroctone olamine

A gentle anti-dandruff ingredient common in European shampoos, with trial results roughly equal to zinc pyrithione but mostly from manufacturers.
conditioning agent

Polyquaternium-10

A positively charged cellulose polymer that coats hair during shampooing, easing wet combing and helping deliver silicones, with some build-up risk.
styling polymer

Polyquaternium-11

A positively charged vinylpyrrolidone copolymer used in mousses, gels and sprays for clear, flexible hold with some conditioning.
conditioning agent

Polyquaternium-7

A synthetic positively charged copolymer used in shampoos and rinse-offs to improve wet combing and feel.
growth stimulant

PP405

An experimental once-daily scalp gel that wakes dormant follicle stem cells; a small phase 2a trial found no blood absorption, and a 600-man trial began enrolling in September 2026.
protein or peptide

Procapil

Procapil is a branded trio of a biotin-linked peptide, apigenin and oleanolic acid sold as a hair-anchoring active, with small studies that are mostly add-ons to other treatments.
botanical

Procyanidin B2

Procyanidin B2, an apple polyphenol, beat placebo in two small related industry-run Japanese trials and one oral apple-extract trial, but nobody has replicated them independently.
humectant

Propanediol

A plant-derived glycol used as a humectant and solvent; no hair-specific study was found.
growth stimulant

PTD-DBM (CXXC5 competitor peptide)

A short peptide that stops the Wnt brake CXXC5 from binding Dishevelled; it sped hair regrowth in mice but has no human data.
botanical

Pumpkin seed oil

A food oil with two small randomised trials for pattern hair loss that look promising but are short, single-centre and unreplicated.
styling polymer

PVP (polyvinylpyrrolidone)

A water-soluble film-forming polymer that gives temporary, washable hold in gels, mousses and sprays.
antiandrogen

Pyrilutamide

A topical androgen blocker from the Chinese company Kintor that reported positive pivotal results in China; no peer-reviewed efficacy paper yet.

R

pathway modulator

Rapamycin (sirolimus)

The longevity-world favourite is a hair paradox: one 2019 mouse study found it starts hair growth, while older and 2013 mouse work found it does not or even delays it, and mTOR-pathway cancer drugs can cause hair loss.
botanical

Red ginseng

Red ginseng and red ginseng oil sped hair regrowth in mice and stimulated cultured papilla cells, but no controlled human trial of ginseng alone for hair loss exists.
botanical

Redensyl

Redensyl is a branded cosmetic blend marketed to wake follicle stem cells, with one small vehicle-controlled trial in a blend and several maker-linked open-label studies.
other

Rice water

Rice water is the starchy water left after soaking or boiling rice, a free and harmless rinse with no clinical hair study behind its growth claims.
immunomodulator

Ritlecitinib

A once-daily pill approved for severe alopecia areata from age 12, which regrows hair in about 1 in 4 people by 6 months and keeps improving for years.
botanical

Rosemary oil

Rosemary oil became the internet's "natural minoxidil" from one small 2015 trial that had no placebo group and has never been replicated.
antiandrogen

RU58841

A topical androgen blocker from the 1990s that grew hair in animal and graft models but has no human efficacy trial and is sold online as a research chemical.
immunomodulator

Ruxolitinib

The JAK1/2 blocker whose first use in three alopecia areata patients in 2014 launched the JAK era for hair; the pill regrows hair in small studies while the cream failed.

S

anti dandruff

Salicylic acid

A scale-loosening ingredient that helps thick flakes and scalp psoriasis plaques and works best paired with an antifungal.
botanical

Saw palmetto

A berry extract with weak DHT-blocking activity that shows small benefits in short, mostly industry-linked trials and clearly less than finasteride in the one head-to-head.
protein or peptide

SCUBE3

A protein released by the hair follicle's command centre only while hair is growing; injecting it into mouse skin was enough to start new growth, with no human data yet.
other

Sea salt (sea salt sprays)

The active in "beach waves" sprays; dissolved salt dries on hair to add grit and bend, but no study has tested its effect on hair.
supplement

Selenium

An essential mineral with no proof that supplements regrow hair, and a well-known cause of hair loss in excess.
anti dandruff

Selenium sulfide

An old, inexpensive anti-dandruff active that new trials suggest works about as well as ketoconazole and has been tested across all curl types.
pathway modulator

Senolytics (dasatinib plus quercetin, fisetin)

Drugs that clear aged "zombie" cells restored the hair-making ability of old human papilla cells in a dish, and fisetin and quercetin grew hair in mice, with no human hair trial.
growth stimulant

Setipiprant

An oral blocker of the PGD2 receptor GPR44 that was tested for male pattern baldness on strong lab data and grew no more hair than placebo in 169 men.
oil or butter

Shea butter

A heavy plant butter widely used on coily hair, with no fibre-science data behind it.
other

Silica silylate

Water-repelling fumed silica used in texturising powders, sprays and pastes for grip, a dry feel and oil absorption.
supplement

Silicon (orthosilicic acid)

A silicon supplement that improved strength and thickness of fine hair in one supplier-run trial.
growth stimulant

SM04554 (dalosirvir)

A topical Wnt-pathway activator tested in about a thousand men with pattern baldness that showed no significant benefit over vehicle.
surfactant

Sodium C14-16 olefin sulfonate

A sulfonate-based cleanser common in sulfate-free shampoos that is still a strong degreaser, so sulfate-free does not always mean gentle.
surfactant

Sodium cocoamphoacetate

A mild two-charge helper surfactant used in baby, sulfate-free and sensitive-scalp shampoos to soften harsher cleansers.
surfactant

Sodium cocoyl glutamate

An amino-acid-based cleanser that was among the best-tolerated surfactants in a 105-patient patch-test study, with no scalp or hair trials yet.
surfactant

Sodium cocoyl glycinate

A glycine-based mild cleanser with one industry body-wash study showing mildness and no scalp or hair studies.
surfactant

Sodium cocoyl isethionate

A mild anionic cleanser, the basis of many syndet bars, with good lab evidence of being gentle on the skin barrier and growing use in sulfate-free shampoos and shampoo bars.
chemical treatment

Sodium hydroxide and guanidine relaxers (lye and no-lye)

Chemical relaxers permanently straighten tightly curled hair; they work, but are linked to scalp burns, breakage and cancer associations still being investigated.
surfactant

Sodium laureth sulfate

The workhorse cleanser of mainstream shampoos, SLS with a short ethylene-oxide chain added, which keeps most of the cleaning and foam and is gentler, with a trace by-product called 1,4-dioxane.
surfactant

Sodium lauroamphoacetate

The lauric-chain version of the amphoacetate family, used as a mild helper surfactant in sulfate-free shampoos.
surfactant

Sodium lauroyl methyl isethionate

A more soluble cousin of sodium cocoyl isethionate used as a mild cleanser in modern sulfate-free shampoos, with no independent studies of its own.
surfactant

Sodium lauroyl sarcosinate

An amino-acid-derived cleanser with good foam and cleaning power that is marketed as mild, though its mildness sits in the middle.
surfactant

Sodium lauryl sulfate

A cheap, strong cleanser and foamer that removes oil very well but is the most irritating common shampoo surfactant, so dermatologists use it as their standard test irritant.
humectant

Sodium PCA

A salt of an amino-acid derivative found in skin's natural moisturising factor, used as a humectant; no hair study was found.
chelator

Sodium phytate

A rice- or corn-derived chelator used in natural shampoos as a preservative booster and iron and copper binder, with no hair trials.
botanical

Spearmint

Spearmint tea lowered free testosterone in two small trials of women with excess hair growth, but no study has tested it for scalp hair loss.
supplement

Spermidine

A natural compound sold as a longevity supplement lengthened human hair follicles grown in a dish at tiny concentrations, but nobody has shown it grows hair on a head.
antiandrogen

Spironolactone

A cheap blood-pressure pill that blocks androgen receptors and is the most widely used off-label hormonal treatment for women's pattern hair loss.
drug with hair side effects

SSRIs and other antidepressants

Antidepressants rarely cause hair loss; in a million-user database, bupropion carried the highest risk and fluoxetine and paroxetine the lowest, but absolute risk is small and depression itself also sheds hair.
drug with hair side effects

Statins (simvastatin, simvastatin plus ezetimibe)

A cholesterol-pill combination regrew hair in a few dramatic alopecia areata case reports, then mostly failed in the open studies that followed; nothing shows topical statins help ordinary balding.
conditioning agent

Stearamidopropyl dimethylamine

A conditioning agent that only becomes positively charged in acidic formulas, used in "quat-free" conditioners; no independent hair data were found.
conditioning agent

Stearyl alcohol

An 18-carbon fatty alcohol, a slightly heavier cousin of cetyl alcohol, used to thicken and soften conditioners; safe at cosmetic levels and rarely allergenic.
other

Stemoxydine

Stemoxydine is a cosmetic compound from L'Oréal pitched as mimicking the low-oxygen niche of follicle stem cells, with no peer-reviewed trial.
oil or butter

Sunflower seed oil

In the classic Marico study sunflower oil did nothing for protein loss, though later work suggests oils of its type can penetrate hair.

T

growth stimulant

TDM-105795

A topical thyroid-hormone-receptor-beta agonist tested in 71 men in 2023; hair counts rose a little more than on vehicle, with no significance reported and no phase 3 since.
botanical

Tea tree oil

A popular natural dandruff remedy with modest evidence, whose oxidised oil is a well-documented contact allergen.
other

Tempol

A free-radical scavenger painted on the scalp before radiotherapy kept hair in guinea pigs and, in a small phase I trial, protected the hair of some brain-radiotherapy patients, but it never became a product.
chelator

Tetrasodium EDTA

The more alkaline, more soluble EDTA salt, with the same chelating job as disodium EDTA and wide use in clarifying and chelating shampoos.
chelator

Tetrasodium glutamate diacetate

A biodegradable, glutamic-acid-based chelator marketed as a greener EDTA replacement, with essentially no hair-specific data.
growth stimulant

Thymosin beta-4

A wound-healing peptide that sped hair growth in rats and mice; the TB-500 vials sold online rest on that animal work, and no human hair trial exists.
drug with hair side effects

TNF inhibitors (adalimumab, infliximab, etanercept)

Anti-inflammatory biologics that can paradoxically trigger alopecia areata or scarring hair loss, even though etanercept regrew no hair in any of 17 patients when tested as an alopecia areata treatment.
immunomodulator

Tofacitinib

The first JAK inhibitor used off-label for alopecia areata; about a third to two thirds of patients regrow hair in open-label studies, but most relapse within months of stopping.
growth stimulant

Topical cetirizine

The common allergy antihistamine, made up as a 1% scalp solution, has several small trials suggesting a modest effect that is weaker than minoxidil.
drug with hair side effects

Topiramate

An epilepsy and migraine pill sometimes floated as a topical hair grower, although nobody has ever tested it on scalp hair; the real hair signals are reversible shedding, one case of overlong eyelashes and a small open trial in compulsive hair-pulling.
growth stimulant

Tretinoin

A prescription acne and anti-ageing cream used off-label as a minoxidil booster because it increases minoxidil absorption, though the one randomised trial found no extra hair benefit.

U

growth stimulant

UK-5099

A laboratory chemical that blocked pyruvate uptake in mitochondria and woke up resting hair follicles on shaved mice, the finding behind the PP405 programme.
immunomodulator

Upadacitinib

A JAK1 pill already approved for other diseases that gave 45 to 55% of people with severe alopecia areata near-full scalp hair in two 2026 trials and is under regulatory review for hair.
supplement

Urolithin A

A gut-bacteria product of pomegranate and walnut compounds, sold as a mitochondria longevity supplement, protected human hair-papilla cells from oxidative damage in a brand-new 2026 company-linked paper, with no controlled human hair trial.

V

growth stimulant

Valproic acid (sodium valproate)

A seizure and mood-stabiliser drug that grew hair as a scalp spray in one tiny trial, but taken by mouth commonly causes hair shedding and is a major birth-defect risk.
supplement

Vitamin A

Too much preformed vitamin A can make hair fall out, so extra vitamin A in a hair supplement is more likely to harm than help.
supplement

Vitamin B12

A real but uncommon cause of hair loss when deficient, with no evidence that extra B12 helps hair if your levels are normal.
supplement

Vitamin D

Hair loss goes with low vitamin D and the receptor is needed for the hair cycle, but no good trial shows supplements regrow hair if you are not deficient.
supplement

Vitamin E and tocotrienols

One small 8-month trial of tocotrienols reported more scalp hairs, with a manufacturer link and no replication.
styling polymer

VP/VA copolymer

A vinylpyrrolidone and vinyl acetate polymer used in sprays, mousses and gels for firmer, less humidity-sensitive hold than plain PVP.

W

growth stimulant

WAY-316606

A lab compound that blocks the Wnt brake SFRP1 and lengthened hair in donated human scalp follicles kept alive in a dish; it has never been tested in a person.

Z

supplement

Zinc

True zinc deficiency causes hair loss that zinc fixes, but zinc has not been shown to regrow hair in people who are not deficient, and too much causes copper deficiency.
anti dandruff

Zinc pyrithione

The most widely used anti-dandruff shampoo ingredient, proven in large trials to cut flaking, though most of those trials were run by the companies that sell it.

Every molecule that touches your hair

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