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A. Klotz, A. zur Mühlen, M. Veeger

Testing the Efficacy of Skin Protectants with the Repetitive Irritation Test

Stockhausen GmbH & Co. KG, Krefeld


In many occupational activities, the skin is put under great stress from frequent washing of hands, working for long periods in damp and wet conditions, and repeated contact with slightly irritative workplace substances such as water, detergents and cooling lubricants. In addition to the technical and organisational measures that can be taken to reduce this skin stressing, skin protectants have also proved to be an effective way of protecting the skin against on-the-job stressing. Such protectants are special cosmetic formulations which are applied to the skin before starting any work, and they should therefore not be confused with skin conditioning or care products, which are meant to be used when the work is finished.

Making any recommendations as to which products to use is frequently guided by the solubility of the protectant in the particular workplace substance. Water-in-oil emulsions or oily ointments are therefore recommended for water-based substances, whereas oil-in-water emulsions, suspensions or gels are put forward as protection against their oil-based counterparts. However, exceptions to this somewhat oversimplified rule have been found in a number of experimental in-vivo human studies [1].

Central to the discussion is whether special stress-matched skin protection for applying before work, and care products matched to the skin condition and applied after work are actually necessary. The view is held in some circles that the efficacy of these products is not based on protecting the skin but on supporting the skin's natural regeneration, and that using suitable moisturising or skin care creams after, and if need be also before work, is therefore perfectly adequate [2, 3].

Various methods are put forward for testing skin protectants in the literature available on this subject [1, 4-13]. The method modified by a working group of the German Clinic for Occupational Dermatology, and based on the repetitive irritation test [7] first described by Frosch and Kurte in 1993 [14], enjoys recognition.

In this model, the skin protectant is first of all put on areas of skin on the volar forearm and the model irritant (0.5% SDS or undiluted toluene) then applied to these areas in Finn chambers twice a day for a period of one week. In addition to the visual score, evaluation also takes into account the barrier function of the skin in the form of the transepidermal water loss in comparison with an area of skin that has not been protected. By modifying the method and not applying the test product until after the irritation, the effect of the product on skin regeneration can also be assessed.

Materials and Methods:

In the tests described, a new kind of multiphase emulsion system of the type water-in-oil-in-water (W/O/W), which had mainly been used only in high-quality facial cosmetics before, was tested on 15 candidates with healthy skin and compared with Vaseline (VAS), a water-in-oil emulsion (W/O) containing panthenol and vitamin E, and a lipogel (LIP = mixture of Vaseline, a wax and a silicone compound as to their protective effect in a repetitive, occlusive irritation test [14, 15] and their influence on skin regeneration where skin irritation had been induced by sodium lauryl sulphate.


Table 1: Skin protection effect of topical formulations in the rep. occl. irritation test (n=15)

Productdelta TEWL [mg/hm²]
W/O/W - 0.5 % SLS8.76 ± 1.18 ***
VAS - 0.5 % SLS11.78 ± 1.63 ***
LIP - 0.5 % SLS13.17 ± 2.28 *
O/W - 0.5 % SLS13.88 ± 1.90 n.s.
0.5 % SLS19.56 ± 2.08

Table 2: Influence of topical formulations on skin regeneration (n=15)

Productdelta TEWL [mg/hm²]
0.5 % SLS - W/O/W8.32 ± 0.83
0.5 % SLS 9.06 ± 1.20
0,5 % SLS — LIP9.33 ± 1.26
0.5 % SLS — O/W9.62 ± 1.05
0.5 % SLS — VAS13.11 ± 2.39

Diagram 1: Influence of topical formulations on SLS-induced skin irritation (TEWL)

In the repetitive, occlusive irritation test (Table 1, Diagram 1), the new protectant of the type water-in-oil-in-water demonstrated the best protective effect against SLS-induced skin damage and significantly superior protection to an anhydrous lipogel.

The tests carried out to determine the influence of the products on skin regeneration (Table 2, no diagram) showed a considerable deterioration in barrier recovery in the case of Vaseline compared with the untreated reference area - but nor did the water-in-oil emulsion (W/O) or the lipogel (LIP) have any positive effect on restoring the barrier function of the damaged skin. The new skin protection formulation (W/O/W), however, showed definite signs, even though they were not significant, of being able to support the attainment of normal skin condition following SLS irritation.


The prevention of occupational skin diseases can be effectively supported by using suitable, special skin protection products. Using the wrong types of preparations, such as an oil-in-water moisturiser, leaves the skin not only inadequately protected, but it can even impair restoration of a natural skin condition after the skin has been exposed to stressing. The example of Vaseline and the hydrophilic W/O/W emulsion shows only too clearly that a product recommendation cannot be made simply on the basis of knowing the hydrophilic or lipophilic properties of the protectant and the substances concerned. The efficacy of each protective product must be tested using suitable in-vivo methods. The method employed in the repetitive, occlusive irritation test is highly suitable for evaluating skin protectants and it should be adopted as a standard method. Additionally, it is possible to assess the main principle of how topically applied skin protectants work (protectively/regeneratively) using the inverted, repetitive, occlusive irritation test.


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Andreas Klotz




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