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.