Enzymes, Detergents and Skin: Facts and Fantasies

D.A. Basketter; J.S.C. English; S.H. Wakelin; I.R. White

Disclosures

The British Journal of Dermatology. 2008;158(6):1177-1181. 

In This Article

Allergy

As is the case with irritation, enzymes have long been recognized as a potential cause of type I allergy of the respiratory tract.[6,7] Within the European Union, enzymes are labelled as potential respiratory sensitizers.[24] Where there has been sufficient exposure, individuals have developed allergic asthma, a situation which did occur to a considerable extent occupationally in the early years of use of enzymes,[4,5,6] but which is now very largely under control.[25,26,27] However, it is still the case that even though enzyme workers may be free of clinical symptoms, a minority still does become sensitized.[26,27] The question to be addressed here is whether there is any risk that any reasonably foreseeable consumer use of enzyme-based products might present any risk of allergy, either for the lungs or for the skin.

Both the induction and the elicitation of allergy require an appropriate degree of exposure, with each of these components of the allergic mechanism being subject to a threshold, i.e. below a certain level of exposure there is no response. Evidence from occupational exposure suggests that the threshold for the induction of allergic reactions to enzymes may be lower than that for elicitation, as a proportion of workers is sensitized, but appears generally to be symptom free.[27,28] Where exposure control is not sufficient, however, then symptoms do occur.[25,28] The occupational exposure limits applied to enzymes that relate to proper controls represent the strictest airborne exposure limits for any material as far as we are aware; typically the limits used are 60ngm−3 or less.[29] However, it seems reasonable to expect that in an uncontrolled consumer environment, then to be safe, exposure levels should be well below these occupational exposure limits, and such does appear to be the case.[30] Industry guidelines on consumer risk assessment for enzymes indicate that a 10-fold lowering of the occupational limit should be appropriate.[29,31,32] The primary point of control which enables such strict limits to be achieved is encapsulation of the enzyme (surrounding the enzyme with a robust inert barrier), so that material cannot become airborne and is unlikely to deliver any significant skin contact.

Industry information indicates that the probable consumer exposure to enzymes is actually much lower than even one-tenth of the occupational limits.[29,30,31,32] Ultimately, though, the demonstration of the effectiveness of controlling enzyme exposure arises not from estimations/measurements of the exposure, but rather from a determination of whether the immune system of exposed individuals has responded by the development of IgE antibodies which would mediate the allergic reaction. The seminal publication on this aspect came from the work of Pepys et al.[33] In this study, 2500 people attending a hospital for allergic investigation of respiratory disease were skin prick tested. Only two patients yielded weak evidence of a positive response to proteolytic enzyme and neither had any suggestion of clinical sensitivity. A similar proportion of individuals was found to have weak, but clinically irrelevant, skin test reactions as part of a screening for a large consumer test (unrelated to laundry products).[34] It is inevitable that when such random screenings are undertaken, then there will be a modest number of inexplicable 'false positives' as the sensitivity and specificity of such tests are established in relation to the guided testing of clinical populations rather than the general population.

Since the original publication, further work has been conducted in other locations to try to confirm an absence of the induction of type I and/or type IV allergic reactivity. For example, a study of 2000 consumers in the Philippines, of whom one third were described as atopic, found no evidence of sensitization, despite a 6% prevalence of hand eczema.[35] This work was enhanced by later results from a long-term follow-up study which had the same outcome.[36] Quite recently (2002), an independent group of investigators representing the North American Contact Dermatitis Group reported on a substantial body of work which examined the question of allergic contact dermatitis to laundry products (i.e. not only to enzymes in such products). Their overall conclusion was that the frequency of allergy to such products was, at best, very low and in all probability presumed positive reactions tended to arise from misinterpretation of skin responses, i.e. they were false positives.[37]

Ultimately, the most telling publication on potential adverse skin reactions to enzyme-based laundry detergents arose from a focused investigation of complainants. The launch of an enzyme-containing washing powder was quickly followed by numerous complaints from domestic users suggesting it was responsible for an adverse skin reaction. Eighty of 255 individuals living in London (U.K.) postal districts who complained to the manufacturer agreed to be investigated by patch and prick testing, and to a use test involving the double-blind wearing of vests washed with the product. The results showed that the enzyme-containing washing powder was not responsible for any dermatological problem, either irritant or allergic in nature.[38]

Such observations as those described above are consistent with what we know of the (patho)physiology of skin allergy. Substances must penetrate the outer skin barrier to reach the viable epidermis and do so in a sufficient quantity and in an appropriate antigenic form in order to activate the immune system in such a manner as to lead to the development of allergic reactivity. By virtue of their size, enzymes are unlikely to penetrate the skin to any great degree;[39] the encapsulation of enzyme in the laundry product means that actual skin exposure will be extremely low. Thus, the only occasions when there is likely to be some degree of exposure is either to the wash solution (when the enzyme encapsulate has dissolved) and/or from any enzyme residues on fabrics. As shown by the studies already mentioned earlier, contact with wash solutions does not lead either to irritation or to allergy; residues on fabrics are also trivially low and do not give rise to any skin effects.[19,20,21,22,38]

On occasions, enzyme-containing laundry products may be misused. Sekkat and colleagues investigated such a situation. In a retrospective study of mechanics in Egypt who had used enzyme-containing laundry granules for personal cleansing (including showering) over at least a 12-month period, no sensitization to enzymes was detected.[40]

As with skin irritation, the overwhelming direction of all the evidence leads to the conclusion that enzymes in laundry detergents are not a cause of skin allergy. This outcome has been confirmed by the prospective studies which have been outlined above.

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