SCALP
Dandruff and itchy scalp, explained
The short answer
Dandruff is your skin overreacting to a yeast (Malassezia) that lives on every scalp and feeds on scalp oil. It is not dry skin or dirt. An anti-dandruff shampoo used regularly controls it. Stop, and flakes return.
Do this
- 1Choose a shampoo with piroctone olamine, selenium sulfide or ketoconazole (a medicated antifungal).
- 2Zinc pyrithione is common in the US, but no longer allowed in EU cosmetics.
- 3Massage in, leave on for the label time, 2 to 3 times a week.
- 4When flakes clear, drop to once a week. Do not stop.
- 5No change after 4 weeks? Try a different active ingredient.
- 6See a doctor for crusts, oozing, hair loss, or scaly patches in a child.
The numbers behind it
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4.4%
Of people worldwide have seborrheic dermatitis, the inflamed form of dandruff. 5.6% of adults (121 studies, 1.26 million people).
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47% vs 19%
Six-month relapse with placebo shampoo versus weekly ketoconazole 2% shampoo in people whose scalp had cleared.
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3 days
How soon yeast, barrier and inflammation markers worsened after switching to a plain shampoo. Visible flakes returned after about 3 weeks (industry study).
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1 week
Dandruff and itch were back to peak about a week after washing, in 60 women with afro-textured hair (L'Oreal study).
For your hair
Curly and coily hair
The scalp can flake while the lengths stay dry. Wash the scalp weekly with the medicated shampoo, then condition the lengths.
Men
In pooled trials of zinc pyrithione shampoo, flaking fell more in men than women (17.5 vs 11.1 points at 4 weeks).
Myths to ignore
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Myth Dandruff means you have a dry scalp.
Truth Dry-scalp flaking and dandruff share one cause: scalp oil, yeast and how your skin reacts. A truly dry scalp is not the usual reason.
Ro 2005 ↗ -
Myth Washing often causes dandruff.
Truth Washing is not the cause. When people switched from an anti-dandruff to a plain shampoo, flakes came back within about 3 weeks.
Locker 2025 ↗ -
Myth Dandruff is poor hygiene.
Truth It is a reaction to a yeast most people carry. Dandruff scalps also have a weaker skin barrier, with far fewer protective fats.
Harding ↗
Made for this
Go deeper
- DandruffDandruff is a common, chronic flaking of the scalp driven by yeast, skin oil and your skin's sensitivity, and an antifungal shampoo controls it well as long as you keep using it.
- Seborrheic dermatitisSeborrheic dermatitis is dandruff with redness and inflammation, and it is controlled rather than cured with antifungal shampoos and, for flares, short-term anti-inflammatory treatment.
- Itchy scalpAn itchy scalp has many causes, and the most common is dandruff or seborrheic dermatitis, so check for flakes first and think about allergy or nerve causes if the skin looks normal.
- Scalp psoriasisScalp psoriasis is an autoimmune skin condition that needs medical treatment, not just a stronger shampoo, and good options exist from topical steroids to biologics.
- Scalp health and oxidized sebumSebum, scalp microbes and inflammation clearly drive dandruff, but there is no human evidence that scalp buildup or oxidized sebum causes hair loss.
- When to see a dermatologistMost gradual thinning is pattern loss you can start treating yourself, but scarring signs, scalp symptoms, patches or sudden shedding should go to a clinician quickly because delay can cost permanent hair.
All studies in this guide (7)
Polaskey MT et al. The Global Prevalence of Seborrheic Dermatitis: A Systematic Review and Meta-Analysis. JAMA Dermatol. 2024
Result: Pooled global prevalence of seborrheic dermatitis 4.38% (95% CI 3.58-5.17%); adults 5.64%, children 3.70%, newborns 0.23%; highest in South Africa (8.82%), lowest in India (2.62%); very high heterogeneity.
Read the study ↗Peter RU, Richarz-Barthauer U. Successful treatment and prophylaxis of scalp seborrhoeic dermatitis and dandruff with 2% ketoconazole shampoo: results of a multicentre, double-blind, placebo-controlled trial. Br J Dermatol. 1995
Tested: 2% ketoconazole shampoo twice weekly, then weekly or alternate-week prevention, versus placebo
Result: 88% had an excellent response; relapse within 6 months was 19% with weekly ketoconazole versus 47% with placebo.
Read the study ↗Locker KCS et al. Understanding the dandruff flare-up: A cascade of measurable and perceptible changes to scalp health. Int J Cosmet Sci. 2025
Result: Biomarker deterioration (Malassezia load, barrier disruption, inflammatory and oxidative markers) appeared after about 3 days and visible flaking after about 3 weeks. Randomized double-blind; industry study.
Read the study ↗Fajuyigbe D, et al. Weekly hair washing: the recommended solution for women with afro-textured hair to alleviate dandruff and scalp discomfort. J Dermatol. 2024
Result: In South African women with afro-textured hair, dandruff and itch returned to their peak about a week after washing.
Read the study ↗Collins LZ et al. Sex-related differences in response to zinc pyrithione shampoo vs. non-anti-dandruff shampoo. Int J Cosmet Sci. 2018
Tested: 1% zinc pyrithione versus a non-anti-dandruff shampoo
Result: Zinc pyrithione beat the control shampoo at all weeks; the 4-week flake-score gap was larger in men (-17.5) than women (-11.1). Unilever authors.
Read the study ↗Ro BI, Dawson TL. J Investig Dermatol Symp Proc. 2005
Result: Dry-scalp flaking, dandruff and seborrheic dermatitis share one cause (sebum, Malassezia metabolism and individual susceptibility) and differ mainly in severity.
Read the study ↗Harding CR, et al
Result: Dandruff scalps had much lower barrier lipids (ceramides, fatty acids, cholesterol) than non-dandruff scalps in UK and Thai samples.
Read the study ↗