[Effects of emulsions on the stratum corneum barrier and hydration]

The appearance of the skin depends greatly on the hydration of the stratum corneum which is regulated by water binding substances of the corneocytes and also by the quality of the stratum corneum lipids. Furthermore these lipids are responsible for the barrier function. In patients with atopic dermatitis, the water binding capacity and the barrier function of the stratum corneum are reduced even in clinically healthy skin areas. Emollients can damage the stratum corneum and lead to desiccation and a disturbance of the barrier. This effect is a result of an increased permeability of the barrier lipids and direct damage to the keratinocytes and corneocytes. The degree of damage of the barrier caused by emollients in dermatological vehicles has not been sufficiently investigated. As suggested by hypothetical considerations, such an effect is not expected and cannot be demonstrated in water-in-oil-emulsions. Oil-in-water-emulsions without glycerol as well as lipophilic and hydrophilic microemulsions do damage the barrier function. Both types of microemulsions additionally lead to a dehydration of the stratum corneum. The damaging effect of oil-in-water-emulsions can be reduced by the addition of glycerol and urea.