RESUMEN
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 rank-sum (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.