How many centimetres does hair grow in a month? Does cutting it make it grow faster?
This answer is a draft. It stays unpublished until legal review and source verification are complete.
"I want long hair but it never grows." "Trimming the ends makes it grow faster." "Is losing 100 hairs a day normal?" Hair growth and hair loss attract plenty of folklore, in Japan as everywhere. Starting from the basics of the hair cycle, this article separates what has evidence from what does not.
Basic hair numbers
| Item | Figure |
|---|---|
| Growth rate | About 0.3–0.4 mm a day, 1–1.5 cm a month, 12–15 cm a year |
| Number of hairs | About 100,000 (varies by person and hair colour; blondes tend to have more, redheads fewer) |
| Daily shedding | 50–100 hairs is normal. Slightly more in autumn (September–November) for many people |
| Life of one hair | 2–6 years (slightly longer in women) |
| Hair cycle | Growth phase (2–6 years, 85–90% of hairs) → regression phase (2–3 weeks) → resting phase (3–4 months, 10–15%) → shedding → growth again |
| Thickness | About 0.05–0.1 mm (Japanese hair tends to be on the thick side) |
| Composition | Protein (keratin) about 80–90%, water 10–15%, lipids, melanin |
Folklore checked
| Claim | Reality |
|---|---|
| Trimming the ends makes hair grow faster | Growth rate is set at the follicle; cutting the ends does not change it. Less breakage and fewer split ends mean length is "kept", so it feels faster. Trimming 1 cm every 2–3 months makes sense for anyone growing their hair |
| Scalp massage speeds growth | Blood flow rises briefly, but evidence that growth rate changes is limited. It relaxes you and helps with cleansing and sebum control. Hard rubbing does harm |
| Losing 100 hairs a day is abnormal | Within the normal range. Persistent loss of 150–200 or more, a visible scalp, or hair coming out in clumps are the signs to see a doctor |
| Hair falls out in the shower, so wash less | What falls is resting-phase hair, and it falls whether you wash or not. Not washing lets sebum and microbes worsen the scalp |
| Pulling out a grey hair makes more grow | It does not (one hair per follicle). But pulling can damage the follicle so nothing regrows — cut it instead |
| Eating seaweed gives you more hair | Iodine and minerals are part of hair's raw material, but eating them does not change count or speed. Shortage of protein, iron or zinc matters far more |
| Supplements (biotin etc.) speed growth | No evidence of effect unless you are deficient. With a deficiency (extreme dieting, iron deficiency), correcting it helps |
| Wearing a hat causes thinning | A poorly ventilated hat worn for hours makes a sweaty scalp worse, but a hat itself does not cause thinning |
- Realistic ways to grow hair long: prevent breakage and split ends (see our separate article on split ends) — do not rub wet hair, go easy on heat, avoid UV, colour or bleach less often, trim 1 cm every 2–3 months. 12–15 cm a year is the ceiling, so shoulder length to long takes 1.5–2 years.
- Nutrition: protein (around 1 g per kg of body weight), iron (menstruating women often run short), zinc, B vitamins. Extreme dieting (losing more than 5% of body weight in a month) causes shedding a few months later.
- Age: growth is fastest in your 20s and 30s; with age hair becomes finer, grows more slowly and has a shorter growth phase. Women's hair often thins after menopause.
- When to see a doctor: a sudden rise in shedding lasting 2–3 months, a visible scalp, round bald patches, eyebrows and body hair also falling, redness or scabs on the scalp. Go to a dermatology clinic (covered by Japanese health insurance). For male- and female-pattern hair loss there are self-pay options (minoxidil, finasteride, etc.).
[Verify] The figures for growth rate, hair count and hair cycle are the general values of hair science. Check against the Japanese Dermatological Association "Guidelines for the diagnosis and management of male- and female-pattern hair loss 2017" [男性型および女性型脱毛症診療ガイドライン2017].
Misunderstanding 1｜Trimming the ends makes hair grow faster
Growth rate is set at the follicle and does not change when you cut. Less breakage simply keeps the length. Trim regularly if you are growing it.
Misunderstanding 2｜Losing 100 hairs a day is the start of baldness
50–100 a day is normal, and more in autumn. See a doctor if 150–200 or more persists or the scalp shows through.
Misunderstanding 3｜Pulling out grey hairs makes more grow
It does not, but pulling can damage the follicle so nothing regrows. Cut at the root instead.
Misunderstanding 4｜Supplements or wakame seaweed give more hair or faster growth
There is no evidence unless you are deficient. Avoiding a shortage of protein, iron and zinc through food matters more.
Misunderstanding 5｜Daily scalp massage makes hair grow
Evidence that it changes growth rate is limited, and hard rubbing does harm. Keep it to cleansing, sebum control and relaxation.
---
Sources
- Japanese Dermatological Association, "Guidelines for the diagnosis and management of male- and female-pattern hair loss, 2017 edition" [男性型および女性型脱毛症診療ガイドライン2017年版]
https://www.dermatol.or.jp/uploads/uploads/files/guideline/
- Japanese Dermatological Association, "Dermatology Q&A: hair structure and the hair cycle" [皮膚科Q&A：毛髪の構造と毛周期]
https://www.dermatol.or.jp/qa/
- Japan Hair Science Association, "Basic knowledge of hair" [毛髪の基礎知識]
https://www.kamiken.org/
⚠️ Editorial note: the source URLs above were identified by search. Our working environment cannot reach go.jp domains, so the contents have not been checked against the text. Verify every source before publication and record who checked it and when.
About this article
What we share here are ideas and everyday practices passed down among people living in Japan, together with general information drawn from public sources. They are not official recommendations, and they are not professional instruction. Practices vary between households and regions.
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