Popular modern hairstyles which tightly braid the hair at the scalp can lead to permanent bald patches, say experts.
“Corn rows” and other styles, like extensions, which pull the hair are to blame, particularly if combined with hair straightening chemicals.
The South African research, published in the British Journal of Dermatology, looked at almost 2,000 adults and children.
A UK dermatologist said that affected hair follicles may never recover.
Specialist braided hairstyles are increasingly popular in the UK, particularly among young people from the Afro-Caribbean community.
The Cape Town-based researchers wanted to find out if they, and other popular cuts such as short “brush-cut” haircuts could cause skin problems.
They found that nearly one in seven children and a third of women suffered from “traction alopecia”, a type of hair loss directly linked to the hair being constantly under tension.
The problem was even more common if chemical “relaxers” had been used to straighten the hair, with one in five children who had used the chemicals suffering hair loss.
The research also found that very short haircuts made men much more prone to developing severe acne on the scalp, thought to be caused by the hair clippers damaging the scalp when pressed hard against the head.
They pointed out that the risk of catching a disease such as HIV or hepatitis could be increased by this type of haircut.
Dr Nonhlanhla Khumalo, who led the research, said: “Traction alopecia is common in women and girls and is significantly linked to hairstyles, particularly when relaxed hair has braids, extensions or weaves attached.
“This can cause unsightly hair loss which is distressing.”
In the UK, dermatologists are reporting similar problems, both due to braiding, and to other popular hairstyles where the fringe is dragged backwards and tied.
Dr Andrew McDonagh, from the Royal Hallamshire Hospital in Sheffield, said: “The best thing is to try to identify the problem early – if this happens for a long time, the hair follicles may be permanently damaged, and hair will not grow back.”
A spokesman for the British Association of Dermatologists added: “Some of these hairstyles might be fashionable, but they can lead to permanent hair loss, which is difficult to cover up and can have a huge impact on a person’s confidence.”