FC04.4 Impact of exposure duration on the induction of contact allergy

Abstract

It has been demonstrated for a wide range of contact allergens that the degree to which sensitisation is induced is highly dependent on the dose per unit area of material applied to the skin. For a given skin area, the concentration of the contact allergen applied may be conveniently expressed as a percentage. However, although a number of other variables affecting induction have been examined, little attention has been paid to the impact of the duration of skin contact. For example, in the human repeated insult patch test the 9 inductions exposures may be applied for either 24h or for a combination of 48h and 72h, the latter ensuring continuous exposure during the 3 week induction period.Under these latter conditions, it is known that the contact allergen p‐phenylenediamine (PPD) sensitises quite efficiently; historical data with 1% PPD in petrolatum resulted in a sensitisation rate of 47/88 (54%). Applying the same dose per unit area, we examined the impact of reducing the exposure time to 9 × 5 minutes spaced over the same 3 week period. Under these conditions, PPD sensitised only 2/102 (2%) of subjects. The data suggest that one route to the limitation of the extent of contact allergy would be to limit the duration of skin exposure.