Headline figure: in a trichology review, wet virgin hair is reported to stretch by up to 30% without damage, to change irreversibly between 30% and 70%, and to break at around 80%.
This page collects the measurable statements about curly and coily hair that two published sources make, so that you can check them and cite them. The main source is a review by Maria Fernanda Reis Gavazzoni Dias in the International Journal of Trichology (2015). The second is the American Academy of Dermatology's care guidance for hair of people of African descent. Neither is a recent study of a new dataset, and we say below where the evidence is thin.
Key figures at a glance
| Measure | Figure | Source |
|---|---|---|
| Stretch of wet, undamaged hair before harm | Up to 30% without damage; irreversible changes between 30% and 70%; fracture at about 80% | Dias, 2015 |
| Hair follicles on the scalp (review estimate) | About 120,000 in Caucasian hair against about 90,000 in people of African descent | Dias, 2015 |
| Cuticle thickness | 6 to 8 scales thick in Asian hair, slightly fewer in Caucasian hair, fewer again in African hair | Dias, 2015 |
| Fibre cross-section | Cylindrical in Caucasian hair; ellipsoid with torsions and diameter changes in Afro-ethnic hair | Dias, 2015 |
| Washing, per the American Academy of Dermatology | Once a week or every other week | AAD |
| Heat pressing, per the AAD | Once a week at most, at the lowest temperature that gives the style | AAD |
| Relaxer touch-ups, per the AAD | Every two to three months, on newly grown hair only | AAD |
How curly and coily fibres differ in structure
Dias reviews how hair fibres differ between groups. Caucasian hair has a cylindrical cross-section. Afro-ethnic hair is described as ellipsoid, with twists along the fibre and changes in diameter, and with a lower water content. The cuticle, the outer layer of overlapping scales, is reported as 6 to 8 scales thick in Asian hair, slightly thinner in Caucasian hair and thinner again in African hair. The review says the thinner cuticle makes African hair more prone to breakage.
The review also gives follicle numbers: about 120,000 in Caucasian scalps and about 90,000 in people of African descent. These are averages for broad groups. Individual hair varies widely, and a head of hair can contain more than one pattern.
Why very curly hair breaks more easily
The review states that the small angle of the waves in very curly hair makes it more susceptible to breakage when it is worked mechanically, and that curly hair is harder to comb without causing frizz. It adds that wet combing of highly coiled hair takes less work than dry combing, and that conditioners and leave-on products reduce friction and make combing easier.
Sebum, the scalp's natural oil, spreads poorly along tightly coiled fibres. The review notes that the sebaceous glands of people of African descent are frequently less active than those of Caucasian people. In practice a scalp can feel oily while the lengths stay dry. Brushing or combing helps move sebum down the hair, and leave-on products can add lubrication.
The stretch figures are given for virgin hair when wet and are not broken down by hair type. They show how much margin any hair has before stretching becomes harmful, not how much a particular curl will tolerate. Our detangling guide covers how to use that margin when you comb.
What the AAD advises for care
The American Academy of Dermatology publishes practical advice for caring for hair of African descent. Its points include:
- Washing: once a week or every other week.
- Conditioner: use it every time you wash, and coat the ends.
- Moisture: a hot oil treatment twice a month.
- Heat: use a heat-protecting product on wet hair before styling. If you press hair with a ceramic comb or iron, do it no more than once a week, at the lowest temperature that gives the style.
- Relaxers: have them applied by a professional, with touch-ups every two to three months on newly grown hair only, and never on hair that has already been relaxed.
- Braids, cornrows and weaves: make sure they are not too tight. The AAD's wording is "pain equals damage".
- When to get advice: see a board-certified dermatologist about changes in hair texture or appearance, including slight thinning.
Our own routine pages build on these points: the wash day routine, deep conditioning and protective styles guides.
What the evidence cannot tell you
- The Dias paper is a review. It summarises earlier work and does not report a new study.
- It groups people by broad ethnic labels. The review itself says data are lacking for some groups, for example for Hispanic patients with curly hair, who may be as sensitive as African hair.
- It gives no ethnicity-specific tensile data, so the 30% and 80% figures should not be read as a limit for any one person's hair.
- Hair type labels such as 3B or 4C are a styling shorthand, not a measurement. See textured hair types and porosity for how far to trust them.
This page is general information and not medical advice. Hair loss, scalp pain or a change in your hair's texture is a reason to speak to a GP or dermatologist.
Frequently asked questions
How much can wet hair stretch before it is damaged?
A trichology review reports that virgin hair can be stretched by up to 30% when wet without damage, that changes become irreversible between 30% and 70%, and that fracture occurs at about 80%. The figures are not broken down by hair type.
How often does the American Academy of Dermatology say to wash African American hair?
Once a week or every other week, with conditioner used every time you wash.
Why does curly hair break more easily than straight hair?
The review says the small angle of the waves in very curly hair makes it more susceptible to breakage when worked mechanically, and that a thinner cuticle in African hair adds to the risk.
Is this page medical advice?
No. It summarises two published sources. Speak to a GP or dermatologist about hair loss, scalp pain or a change in your hair's texture.