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Evaluating Water Permeability and Occlusion in Wound Dressings and Topical Cosmetics
By: Hongbo Zhai, MD, and Howard I. Maibach, MD, University of California
Posted: June 30, 2009, from the July 2009 issue of Cosmetics & Toiletries.
Occlusion refers to covering the skin by any means of film or substance;1 this extends to wound dressings, which can be differentiated as being fully occlusive or semi-occlusive. Wounds are either covered or left exposed to air and while studies have shown that occlusion may speed the healing process of wounds faster than air exposure,2,3 completely occlusive dressings have some disadvantages, particularly when compared to semi-occlusive dressings.4 For instance, if bacteria are trapped under the wound dressing, the fully occlusive dressing provides a warm and moist environment for the bacteria to reproduce, potentially leading to infection.5
On the other hand, a semi-occlusive dressing presumably allows more water and oxygen transfer. Thus, bacteria multiply less. Some experiments have shown semi-occlusion to be preferable for wound healing.5,6 Therefore, water vapor may be a differentiating variable between these dressings and is also an indicator of epidermal lipid synthesis, a signal for recovery.7,8
The present study uses an evaporimeter to measure the degree of water loss from in vitro skin samples covered by occlusive and semi-occlusive wound dressings to serve as a model for determining the effectiveness of occlusive cosmetic formulations. The purpose of this work was to develop a model for determining the effectiveness of occlusive cosmetic formulations.
As an example, acrylates/octylacrylamide copolymer is a hydrophobic, high molecular weight carboxylated acrylic copolymer that is inherently moisture resistant and as such can be used in waterproof sunscreens and a variety of creams and lotions. Its film-forming properties help to maintain active ingredients on the site of application by imparting resistance to abrasion or rub-off. This material was compared with other occlusion films to determine its potential as a wound healing dressing.
Materials and Methods
Wound dressings: Laboratory filma, a putative occlusive membrane; adhesive bandagesb, presumably semi-permeable from their fabric covering; and acrylates/octylacrylamide copolymerc were purchased for the study.