Testing for Penetration of the Skin Barrier

Emphasis on product performance has tended to focus on the actives(s) within a product, with the actual formulation itself being given secondary consideration. Active ingredients for skin care require effective vehicles for their delivery across the stratum corneum in order to achieve the benefit claimed. Sunscreens however, require effective vehicles that will prevent penetration beyond the upper layers of the stratum corneum to achieve their maximum potential in screening out UVA/UVB yet having a uniform spread for maximum sun protection and safety.

The challenge arises when verifying and evaluating the effectiveness of formulations in delivering these actives to the place, for the time and in the quantity necessary to maximize performance. These challenges will be discussed, together with examples of clinical methods that can be employed to prove the effectiveness of formulations as delivery systems.

Under normal conditions the barrier of the skin may vary considerably in terms of age, season and anatomical site. Minimal differences are seen within race and sex, however, there are differences between skin types. In addition, the barrier function in diseased skin is often impaired.

Anatomical site: Regional variation in barrier properties have already been demonstrated.

Age: During development, barrier function is markedly changing. The barrier of the skin in pre-term infants is impaired, which is accompanied by increased TEWL and a large heat loss. By contrast, full-term infants have a well-developed barrier, which thereafter does not significantly change. Only people beyond 70 years of age (on average) have been reported to show decreased TEWL.

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