Implementation of a standardized human in-vivo protocol for efficacy testing of skin protective products against lipophilic occupational irritants

Status:

completed 06/2012

Aims:

Skin protection products, or so-called pre-work creams, are cosmetics that are used at workplaces to prevent or diminish irritant hand dermatitis, whenever gloves are inappropriate. Such products have been proven to be effective against the irritant impact of so-called wet work and contact to water soluble irritants such as detergents. They are as well marketed with the claim to be beneficial against irritation caused by lipophilic work substances, such as solvents. However, evidence of their actual properties against lipophilic irritants is missing to date, at least as far as results from repetitive in vivo efficacy tests are considered.

Activities/Methods:

In the scientific project presented here, a repetitive irritation model with lipophilic irritants was developed, which enables simultaneous efficacy testing of several preparations on human skin in vivo. Two occupationally relevant organic solvents, one aliphatic (n-octane, CAS-Nr. 111-65-9) and one aromatic (cumene, isopropylbenzene, CAS-Nr. 89-82-8), were chosen as model irritants, after toxicological reviewing. Methods were implemented to quantify the degree of irritation achieved by using capacitance measurements on the skin surface together with clinical grading. Statistical parameters were developed that allow to prove and compare the protection efficacy of preparations.

Results:

Two subsequent blinded studies using this test protocol with commercial products claimed to "protect against irritation from solvents" revealed that two out of six products did not only fail to protect, but indeed aggravated skin irritation. Two other products offered significant protection only against cumene-induced stratum corneum dehydration. Altogether, none of the products offered satisfactory protection against octane. Meanwhile, publications on the toxicological profile of cumene suggest that this substance can no longer be recommended as a model irritant. The project was therefore terminated and a multicentre validation study was cancelled. Subsequent work outside the given project frame is needed to establish a new model irritant to replace cumene.

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