The hair growth cycle

Key takeaways

• Every scalp follicle runs its own clock. It cycles through anagen (growth, years), catagen (shutdown, about 2 weeks), telogen (rest, about 2-3 months), exogen (the club hair is actively released) and often kenogen (the follicle sits empty for months before regrowing). Because follicles are out of sync, you never shed everything at once Natarelli 2023, Rebora and Guarrera 2002.
• About 85-91% of scalp hairs are growing at any moment and roughly 9-15% are resting Natarelli 2023.
• Scalp hair grows roughly 0.26-0.41 mm a day depending on ancestry, which is about 0.8-1.2 cm a month. African-born adults grew slowest and East Asian hair fastest in multi-country industry studies Loussouarn 2001, Loussouarn 2016.
• How long your hair can get is set mainly by how long anagen lasts, which is largely inherited (the FGF5 gene is one proven switch), and then by how much the ends break off Seago and Ebling 1985, Higgins 2014, Khumalo 2000.
• "50-100 hairs a day" is a rule of thumb, not a measured cut-off. Published figures run from about 50 to 150 a day Sinclair 2015. In the only longitudinal daily count we found (14 UK men), shedding averaged about 60 a day at its late-summer peak, more than double the winter level Randall and Ebling 1991.
• Shedding is seasonal. Telogen counts peak in summer to early autumn in European men and women and in Chinese adults, so a late-summer rise is normal Kunz 2009, Courtois 1996, Liu 2014.
• A shedding surge 2-4 months after a fever, birth, crash diet, surgery or major stress is the classic telogen effluvium timeline Harrison and Sinclair 2002.
• Pattern hair loss is mainly hair getting finer and shorter-lived, not hair falling out faster. Anagen shortens, follicles miniaturize and the empty gap between hairs lengthens. In Japanese men aged 25 or older, those with pattern loss had similar hair counts to those without but far fewer thick hairs Courtois 1994, Ishino 2014.
• Women who report more shedding but no visible thinning are not automatically fine: in one dermatologist's biopsy series, about 60% of them turned out to have early pattern hair loss Sinclair 2015.
• Normal aging looks like a mild version of balding: anagen gets shorter, the thickest hairs get thinner and follicles stay empty longer Courtois 1995.

The phases

• The empty-follicle gap is also called the hair eclipse or latency. Shedding and the start of the next anagen are controlled separately, so a shed hair is not always replaced at once Pierard-Franchimont 2001, Pierard-Franchimont 2003.
• Body sites differ hugely. Eyebrow anagen lasts only about 2-3 months Natarelli 2023. On the thigh, anagen averaged 54 days in men and 22 days in women Seago and Ebling 1985.
• A normally shed telogen hair has an even shaft and a pale, club-shaped bulb. That small white root is normal and does not mean the follicle was pulled out or has died Steck 1978.

How many hairs, and how fast they grow

The cm/month conversions are our arithmetic (µm/day x 30).

Maximum length

• Final length is roughly growth rate times anagen duration. On the thigh, men's hairs ended up three times longer than women's, mainly because anagen lasted 2.46 times longer and partly because they grew 1.22 times faster Seago and Ebling 1985.
• Anagen length is genetically controlled. Families with FGF5 mutations have extremely long eyelashes and longer forearm hair, with more follicles in anagen Higgins 2014.
• Illustrative arithmetic (ours): at 0.35-0.40 mm/day, a 2-year anagen gives about 25-29 cm (roughly shoulder length) and a 6-year anagen about 77-88 cm.
• Visible length also depends on breakage. In 12 African volunteers whose hair had not been cut for at least a year, 10-16% of shafts had knots (versus 0.15% in other groups) and electron microscopy showed repeated breaks Khumalo 2000. For tightly coiled hair, "my hair doesn't grow" often means the ends break as fast as the roots grow. See hair by ancestry.

Normal shedding: what the numbers are

• Women: 50-150 hairs over 24 hours, most of it unnoticed Sinclair 2015. A review gives 100-150 telogen hairs per day, citing older literature Natarelli 2023.
• Measured seasonal peak: about 60 per day in August-September, more than double the winter rate (14 healthy UK men aged 18-39, counted every 28 days for 18 months) Randall and Ebling 1991.
• 60-second comb count: a mean of about 10 hairs at ages 20-40 (range 0-78) and 41-60 (range 0-43), stable on consecutive days and 6 months later (60 healthy men, convenience sample) Wasko 2008.
• Modified wash test (a clinic tool): 100 or more hairs shed best matched a clinical diagnosis of telogen effluvium, and 10% or more short hairs (3 cm or less) pointed to pattern loss. Agreement with clinical diagnosis was only moderate (kappa 0.53, 100 patients) Rebora 2005. Test-retest reliability over 4 weekly tests was good to almost perfect except total counts in normal subjects (25 subjects) Guarrera 2011.

Why the numbers are fuzzy: shedding varies with season, time since the last wash or brush, and hair length. Longer hair, bathroom lighting, floor color and anxiety all change how much shedding people notice Sinclair 2015. Among people diagnosed with chronic telogen effluvium, 97.5% were women. A 2023 systematic review suggests some cases may reflect a preoccupation with normal shedding in anxious long-haired people, while others are early pattern loss or an unrecognized trigger Daunton 2023.

Seasonal shedding

• UK men: anagen peaked above 90% in March and fell to a trough in September, with the most shedding in August-September Randall and Ebling 1991.
• Ten French men followed 8-14 years: telogen peaked at the end of summer and start of autumn, and some had two peaks a year Courtois 1996.
• 823 Swiss women with hair-loss complaints: the most telogen hairs in summer, a smaller peak in spring, the fewest in late winter Kunz 2009.
• 41 Chinese adults followed monthly: telogen rose in August-September, a smaller effect than in Europeans and within normal limits Liu 2014.

When shedding is a problem: telogen effluvium in brief

A stress pushes many anagen follicles into rest early, and they shed together about 2-4 months later Harrison and Sinclair 2002. Common triggers include major weight loss, childbirth, high fever, surgery, illness, severe stress and stopping the pill. Fullness usually returns within 6-9 months unless the trigger persists. One expert groups the condition into three mechanisms: premature teloptosis, collective teloptosis and premature entry into telogen Rebora 2016. See telogen effluvium.

Miniaturization: how pattern hair loss works

• In male pattern hair loss, follicles in a pre-programmed pattern progressively shrink from terminal to vellus-like and their anagen shortens. How androgens trigger this is still not fully explained Altendorf 2026. In women, androgens are also thought to drive miniaturization by shortening anagen Kearney 2026. Both are recent reviews.
• Ten men tracked for about 15 years (nearly 10,000 hair cycles) showed a growing share of hairs with short anagen, a parallel fall in diameter and longer empty gaps before regrowth Courtois 1994.
• Men's biopsies: pattern-loss sections averaged 22 terminal and 13 vellus hairs. Among 44 men treated with minoxidil, fewer than 2 follicular structures per mm2 predicted no regrowth Whiting 1993.
• Women with female pattern hair loss (42 women, 3 biopsies each): terminal follicles fell from 263 to 96 per cm2 between the mildest and most severe grades, vellus follicles rose from 33 to 71, the terminal-to-vellus ratio dropped from 12.8 to 2.3 and telogen rose from 13.7% to 31.4%. Total follicles fell from 317 to 243, so miniaturization ends in follicles disappearing Messenger and Sinclair 2006.
• In 369 Japanese men aged 25 or older, those with pattern loss had about the same density as those without, but fewer thick hairs (over 80 µm) and more vellus hairs (under 40 µm) Ishino 2014.

See androgenetic alopecia.

Aging without pattern loss

In men followed 8-14 years, anagen shortened, shaft diameter fell (most in the thickest hairs) and the gap between losing a hair and regrowing one lengthened, resembling balding only milder Courtois 1995. In Japanese women, density, anagen ratio and growth rate all declined after the 40s Tajima 2007.

What it means for your hair

• Curl and ancestry: tightly coiled hair grows more slowly on average and breaks more readily, so length goals depend more on keeping the ends than on speeding up growth Loussouarn 2001, Khumalo 2000.
• Hair length: long hair makes the same number of shed hairs look like far more on the brush, pillow or drain Sinclair 2015, Daunton 2023.
• Washing frequency: the wash test relies on hairs released since the last wash coming out at the next one Rebora 2005. Our inference is that people who wash less often see bigger clumps per wash without losing more hair overall. See washing frequency.
• Thickness and density: pattern loss shows first as thinner and fewer thick hairs rather than missing hairs. See strand thickness and hair density.

Myths and facts

• "Losing 100 hairs a day means you're going bald." Published normal ranges run up to 100-150 a day; pattern loss is driven by miniaturization Sinclair 2015, Ishino 2014.
• "The white bulb on a shed hair means I pulled out the root and the follicle is dead." It is a normal club root and the follicle stays Steck 1978.
• "Everyone's hair could reach waist length if they stopped cutting it." Maximum length depends on each person's anagen duration and on breakage Higgins 2014, Khumalo 2000.
• "More hair in the brush in autumn means something is wrong." Late-summer and autumn telogen peaks are documented in healthy people Kunz 2009, Randall and Ebling 1991.
• "No visible thinning, so extra shedding can't be pattern loss." About 60% of women with more shedding but no visible thinning had pattern loss on biopsy, in one specialist's series Sinclair 2015.
• "Shed hairs are replaced immediately." Follicles can sit empty for months, and the gaps lengthen with age and in pattern loss Rebora and Guarrera 2002, Courtois 1995.

Practical points

• Judge shedding against your own baseline and the season, not a magic number. If you want a number, use one standardized method repeatedly, such as a 60-second comb count done the same way each time Wasko 2008, and compare across months.
• A sudden diffuse shed 2-4 months after a trigger is usually telogen effluvium and usually recovers in 6-9 months. See a doctor if it lasts longer than about 6 months, comes in patches, comes with an itchy, painful or scaly scalp, comes with loss of eyebrows or body hair, or if your part widens, your hairline recedes or you see more short fine hairs.
• For length goals, protect the ends from heat, chemicals and rough detangling. Growth rate itself mostly reflects genetics, age and ancestry.
• If you are worried about pattern loss, track part width, crown and temple photos and the share of short fine hairs rather than shed counts. See hair loss scales, hair density and taking a good hair photo.

Bottom line

Hair cycles asynchronously, so some shedding every day is normal and the exact number varies by season, length and how you count. Pattern hair loss is mostly a shrinking of hairs, not an increase in shedding, so look at part width and thickness over time rather than counting hairs in the brush. Much of the data is from small studies or one company's labs.