oa South African Medical Journal - The pH of lye and no-lye hair relaxers, including those advertised for children, is at levels that are corrosive to the skin - research

Volume 109 Number 12
  • ISSN : 0256-9574
  • E-ISSN: 2078-5135



Background. Hair relaxers are used by up to 70% of females of black African ancestry. Occupational safety regulations list a pH ≥10.5 as irritant and a pH ≥11.50 as corrosive to the skin.

Objectives. To determine the pH of all relaxers sold on the South African market and whether it is lower in no-lye relaxers and those marketed for children.

Methods. Relaxers were purchased from retailers in Cape Town, but more than half (54%) of the 39 brands tested were international. The pH was determined using a benchtop pH meter with an electrode for emulsions. Three pH readings were done over 3 consecutive days for each sample, and the average was used for data analysis. Differences between relaxers were analysed using Kruskal-Wallis, Wilcoxon ranksum (Mann-Whitney) and two-sample t-tests (p<0.05).

Results. The median pH of all relaxers (calcium hydroxide, lithium hydroxide and sodium hydroxide) was 12.36 (interquartile range 12.10 - 12.62). The active ingredient was sodium hydroxide (lye or caustic soda) in 63% of the total of 121 relaxers (6/76 (7.9%) of these marketed for children). Lithium hydroxide and calcium hydroxide (no-lye) relaxers comprised 17% and 20%, respectively. No difference in pH was found between relaxers marketed for adults and those for children (sodium hydroxide p=0.2703, lithium hydroxide p=0.6787 and calcium hydroxide p=0.1048) or between lye (sodium hydroxide) and no-lye (calcium hydroxide) relaxers (p=0.2740). Furthermore, 64/70 (91%) of sodium hydroxide relaxers for adults and 4/6 (67%) of those for children were sold packaged without a neutralising shampoo.

Conclusions. The pH of all the relaxers tested was at levels deemed corrosive to the skin and may contribute to the high prevalence of alopecia in females with afro-textured hair. A review of permissible safe pH levels for cosmetic use is warranted.

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