Erroneous gender differences in axillary skin surface/sweat pH

• Published in: International journal of cosmetic science 2001-04, Vol.23 (2), p.99-107
• Main Authors: Burry, J S, Coulson, H F, Esser, I, Marti, V, Melling, S J, Rawlings, A V, Roberts, G, Mills, A K
• Format: Article
• Language: English
• Subjects: antiperspirant; Applied sciences; axilla; Chemical industry and chemicals; Cosmetics, toiletries; eccrine gland; Exact sciences and technology; skin pH; sweat pH; thermoregulation; Washing products. Cosmetics and toiletries. Perfumes
• ISSN: 0142-5463; 1468-2494
• DOI: 10.1046/j.1467-2494.2001.00085.x

Synopsis Assessing accurately the pH of axillary eccrine sweat is of vital importance in the antiperspirant industry. Eccrine sweat pH is a critical parameter in determining the effectiveness of antiperspirants; antiperspirant salts dissolve in sweat and diffuse into the sweat glands, where the resultant acidic solution hydrolyses in more alkaline sweat forming an amorphous metal hydroxide gel, thereby restricting the flow of eccrine sweat. Comparison of the skin surface and sweat pH of males and females reported in the literature shows that, although consistent male/female differences have been observed on the forearm, determination of significant gender‐based pH differences across other sites are less conclusive. Studies on the back and infra‐mammary regions exhibited significant gender differences in skin surface pH, whereas those on the forehead, cheek, neck and inguinal area showed no such difference. With regard to the axilla specifically, four studies have been reported, three showing no significant difference in axillary skin surface pH and one indicating that females have an eccrine sweat pH of 7 and males have a sweat pH of 5.6. This paper describes a series of carefully controlled studies aimed at assessing potential gender differences in eccrine sweat and skin surface pH following exposure to a variety of temperature, humidity and time conditions. The results highlight the importance of controlling precisely the time of investigation, site of measurement and, most importantly, the necessity to pre‐equilibrate samples in 40 mmHg carbon dioxide (equivalent to arterial CO2 tension (pCO2)) before determining sweat pH. When these parameters are controlled no gender differences in axillary sweat or skin surface pH are observed. Large differences in eccrine sweat and skin surface pH are found, however, between the vault (hairy region) and fossa (non‐hairy region) of the axilla. Résumé La détermination précise du pH de la sueur au niveau des aisselles est de première importance dans l’industrie des antitranspirants. Le pH de la sueur est un paramètre clef affectant l’efficacité des produits antitranspirants; ceux‐ci agissent par diffusion d’une solution d’actifs antitranspirants dans les glandes sudoripares où ils sont hydrolysés et forment un gel amorphe d’hydroxyde métallique limitant ainsi le flux de transpiration. Une comparaison des données publiées dans la littérature sur le pH de la peau et de la sueur chez les hommes et les femmes, révèle que b