Negatively charged hair and skin proteins (None)

The negatively charged surfaces of hair and skin proteins primarily consist of keratins and associated lipids that exhibit an anionic character at physiological pH. This negative charge arises because the isoelectric point (pI) of hair and skin proteins is typically between pH 3.1 and 4.5, while the natural pH of the skin surface (the acid mantle) is approximately 4.7 to 5.7 and hair is frequently exposed to neutral water (pH 7.0) during cleansing [1, 2]. At these pH levels, the carboxylic acid groups of amino acids like glutamic and aspartic acid, along with cysteic acid groups formed from the oxidation of disulfide bonds, are deprotonated, resulting in a net negative surface potential [2, 3]. This physicochemical property is the primary target for cosmetic and dermatological delivery systems, particularly conditioners and emollients that utilize cationic (positively charged) surfactants and polymers [2, 4]. These cationic agents electrostatically bind to the damaged, anionic sites of the hair cuticle or stratum corneum, forming a protective film that reduces friction, eliminates static electricity, and improves the tactile and mechanical properties of the keratinized tissue [1, 4]. References: [1] Robbins, C. R. (2012). Chemical and Physical Behavior of Human Hair. Springer Science & Business Media. [2] Gavazzoni Dias, M. F. (2015). Hair Cosmetics: An Overview. International Journal of Trichology, 7(1), 2–15. [3] Ali, S. M., & Yosipovitch, G. (2013). Skin pH: From Basic Science to Basic Skin Care. Acta Dermato-Venereologica, 93(3), 261-267. [4] Bhushan, B. (2010). Biophysics of Human Hair: Structural, Nanomechanical, and Nanotribological Studies. Biological and Medical Physics, Biomedical Engineering.

Other names

Anionic keratin surfacesAnionic surface of the stratum corneumHair fiber surface chargeNegative surface potential of keratinized tissues

Electrostatic adsorption of cationic (positively charged) molecules to anionic (negatively charged) protein sites to reduce friction, neutralize static, and restore lipid barriers.