Effects of four soaps on skin trans-epidermal water loss and erythema index.

Traditional alkaline soap increased TEWL and skin erythema, which are signs of prolonged damage to the skin barrier. However, the effects of other formulations were transient, and TEWL returned to baseline at 72 hours. Creamy soap even showed a relative protective effect (decrease in erythema index compared to baseline), probably due to the lanolin content of the formulation.