Reduced allergy rates in atopic eczema to contact allergens used in both skin products and foods: Atopy and the 'hapten-atopy hypothesis'

Background: Food allergy is strongly associated with atopy. This retrospective study investigates whether atopic status affects responses to contact allergens also found in food. We compared incidences of atopic dermatitis/eczema (AD) in subjects who were patch-test positive (PT+) to diallyl disulfide from handling garlic and parabens used as a skin cream/ointment and food preservative with the incidence in those subjects who were PT+ to chemicals encountered at skin surfaces (lanolin and nickel). Results: 36 658 patients with eczema/dermatitis were patch tested (1980-2006). 10 326 (28.2%) had AD. 13/83 (15.6%) PT+ subjects to diallyl disulfide/garlic had AD (AD/total population versus AD/diallyl disulfide PT+, P = 0.011). 54/239 parabens PT+ had AD (22.6%), while 181/608 lanolin PT+ had AD (29.8%) (P <0.05). Conclusions: Contact allergy to haptens with oral and skin exposure is reduced in AD compared with non-AD, unlike food protein hypersensitivity. Lanolin frequency was not decreased. Possible explanations include (i) confounding factors, e.g. AD subjects handle garlic less than non-AD subjects, or (ii) AD patients tolerate haptens efficiently, secondary to their atopic status, or (iii) oral tolerance of haptens antagonizes tolerance of food proteins, contributing to development of atopy (hapten-atopy hypothesis). The recent upsurge of atopy took place when gut exposure to haptens in processed foods increased dramatically. © 2008 The Authors.