Occlusive dermal preparations

Dermal absorption is influenced by several factors, e.g. the physico-chemical properties of the substance, vehicle, occlusion, concentration, exposure pattern and skin site of the body (ECETOC, 1993 Howes et al., 1996 Schaefer and Redelmeier, 1996). Despite the fact that guidance exists for the conduct of dermal absorption studies (USEPA, 1998, 2004 OECD, 2004a,b,c), there continues to be discussion on some experimental details. In order to harmonize the use of dermal absorption data in human risk assessment within the EU, a guidance document was prepared by the Commission (EC, 2002). 

After leaving the solution to rest for 24 hours and filtering it, UV exposure was what made it effective Solutions not exposed to UV did not appear to work. The skin was also prepared by UV exposure, and the solution was applied five times, leaving each coat to dry before the next application. Urkov then applied an occlusive mask. This mask allowed the superficial layers to hyperhydrate by blocking transepi-dermal water loss (TEWL). The hyperhydration dissolved the salicylic acid that would have precipitated on the skin without occlusion and could not have penetrated, as only the acids in solution can readily penetrate the skin barrier. He then applied zinc stearate powder (which is antiseptic and anti-inflammatory). The erythema subsided in 5-6 days and exfoliation was superficial. The solution can be kept in the fridge for 10 days. 

Lip Eyelid formula is a phenol peel that I first developed to increase dermatological safety and to achieve results without any occlusion on the sensitive skin of the eyelids. The same solution was then applied to the wrinkles around the mouth and then to the whole face, but with 24 hours occlusion in these two indications. It is an oil solution of phenol at over 60%. Four different oils are used in the various stages of the product s preparation. The aim of the oily formulation is to slow down the penetration of the phenol through the skin and to improve dermal and epidermal maceration. It limits the toxicity of phenol by saturating the biochemical hepatic detoxification pathways more slowly. 

With emphasis on safety evaluation applications, the use of radiotracers in rat and mouse dermal absorption studies are discussed. A multi-tiered experimental strategy is proposed containing judgement points providing akin absorption, tissue depletion and animal excretion rates in a cost effective manner. Techniques described include occlusive and non-occlusive treatments, sample preparations and data collection. Typical data is shown for herbicides and insecticides. 

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