All hair relaxers sold locally would be classed as dangerous if they were subject to workplace legislation.

The Occupational Health and Safety Act says any alkaline substance with a pH value of 11.5 or above is hazardous and corrosive.

A new analysis of 121 hair relaxers sold in SA found a minimum pH value of 11.75 and a maximum of 13.17.

The average was 12.34.

Scientists from the hair and skin research laboratory at the University of Cape Town, who reported their findings in the December edition of the SA Medical Journal, say the Foodstuffs, Cosmetics and Disinfectants Act should be amended so that it regulates relaxers.

"The cosmetics regulatory framework has no pH restrictions for relaxers. There is a need for this framework to be revised," said Nonhlanhla Khumalo, head of dermatology at UCT's medical school.

The hair and skin research laboratory at the University of Cape Town tested 121 hair relaxers that they bought from Cape Town shops.

The strong alkalis used in hair relaxers - usually sodium hydroxide - are present in greater concentration than in household cleaning products, they found. "Bleach has a pH of about 11, oven cleaners about 12 and drain cleaners 12-13. The pH of products used by women with afro-textured hair and on children is, therefore, equivalent to that of drain cleaners," researchers said.

Khumalo has campaigned for safer cosmetic products aimed at black women for more than a decade, and said in the new paper that 78% of black schoolgirls and 49.2% of black women used relaxers.

They were strongly associated with hair loss (alopecia), as well as scalp irritation, burns, scarring and allergic reactions, she said. Khumalo and colleagues Ntombi Sishi and Jennifer van Wyk found that 68 of the 76 sodium hydroxide relaxers on the market - including four targeted at children - were not packaged with a neutralising shampoo.

Even some of those that included shampoo provided an amount that was probably too little to work properly. They also found no difference between relaxers marketed for adults and children, and no difference in the pH values of relaxers of different strengths.

On top of all that, relaxers were probably being used too often, they said.

A study in Nigeria had reported women using them 11 times a year, while manufacturers said they should be used for a maximum of 8.7 times.

In 2008, Khumalo and colleagues found that almost one in three women who used relaxer every seven weeks were at moderate to severe risk of traction alopecia. This is hair loss caused by hair being pulled, often as a result of tight braids, ponytails or pigtails.