Abstract
It is well known that a subtle balance exists between consumer desire to use hair dyes of various kinds and the sensitizing effects of particular dye ingredients. Of these, p‐phenylenediamine (PPD) is the mostly commonly reported contact allergen and which serves as a general model for hair dye allergy. PPD is reported as a strong sensitizer in all predictive tests; it is fairly commonly identified as a contact allergen in diagnostic patch testing, with relevance to hair dye ACD being about 50%. Whilst it may not be possible always to eliminate, or even greatly reduce, the extent to which sensitisation is induced, a final opportunity for limiting the degree of ACD occurs at the elicitation phase. Here, ensuring the extent of skin exposure is below the level at which all except the most strongly sensitized will react can provide clear consumer benefits. To achieve this aim, it is necessary to ensure a full appreciation of the variables impacting the elicitation of ACD exist. To this end, series of investigations of the elicitation of p‐phenylenediamine (PPD) sensitization has been conducted. In particular, the impact of duration and frequency of exposure on elicitation has been studied. Using groups of PPD sensitized volunteers, in patch tests and repeated open application tests, we have shown that exposures of only a few minutes are often without consequence in such individuals, except where the exposure is often repeated and/or the individual is highly allergic. With volunteers who were 1+ or 2+ positive to the diagnostic patch test, and where exposure to PPD was at 0.5%–1.0% in a short contact rinse‐off hair colouring product, no scalp reactions were experienced. It is our view that the establishment of safe exposure limits to contact allergens should be based wherever possible on a detailed assessment of the risk to sensitized humans.
Published Version
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