The irritation potential and reservoir effect of mild soaps

Identification and reduction of external noxious factors is one key point in the strategy for the treatment and reduction of contact dermatitis. A wide variety of soaps on the market are claimed to be suitable for the use on sensitive skin due to their mildness. The aim of the present study was to illustrate possible differences in the irritation potential of 8 products and to investigate whether surfactant residues may form an irritant reservoir on the skin. The study was double-blind, randomized using healthy human volunteers. The inherent capacity of the products to induce irritation was determined using conventional patch test technique, whereas detection of potential surfactant residues on the skin was done using a methodology developed in the 1960s for detection of the corticosteroid reservoir in the stratum corneum. The method comprised the release of active substance from the stratum corneum reservoir by occlusion of the skin with an aluminium chamber, followed by evaluation of the biological response. In the present study, the soap-treated area was rinsed with water and then occluded. Instrumental measurements of the transepidermal water loss and superficial skin blood flow served as indicators of the injurious effects of the products. The results showed large differences in irritation potential between the products, and some of them demonstrated considerable damaging effect. Moreover, the study proved the presence of barrier-impairing residues on the skin after rinsing with water. Subclinical skin damage can make the skin vulnerable to further irritation and delay recovery of chronic irritant contact dermatitis.