The gentleness of surfactants on human skin, eyes and hair, especially on skin and eyes, is a difficult concept to define, and so far there is still no uniform standard. The irritability or sensitization of surfactants to mucous membranes is mainly caused by three factors:
(1) Dissolvability refers to the degree of dissolvability of surfactants to the skin's own moisturizing components (such as moisturizing factor NMF), intercellular lipids and free amino acids and fats in the stratum corneum. Excessive dissolution of these ingredients will destroy the skin's oil and surface layer, reduce the skin's water retention ability, and cause cells to fall off into zest, resulting in skin tightness, tingling or dryness. What's more, in addition to the peeling effect of the surfactant on the cell, it also has a dissolution effect on the cell, such as SDS is a very effective dissolution agent of the biofilm.
(2) Penetrability refers to the ability of surfactants to penetrate through the skin, and this effect is thought to be one of the causes of various skin inflammation. The infiltration of surfactants changes the original structural state of the skin and the compatibility between adjacent molecules, resulting in contact dermatitis, dermatitis, skin irritation and even allergic reactions, causing erythema and edema on the skin. Cations were the most active surfactants, anions were the second, and nonionic and zwitterionic surfactants were the least.
(3) Reactivity refers to the adsorption of surfactant on protein, resulting in protein denaturation and changing skin pH conditions. The experimental results show that the reactivity of PEG is lower than that of LAS and other anions.