Thumb-sucking or nail-biting in childhood led to a reduction in atopic sensitisation but not asthma or hay fever

ed from: Lynch SJ, Sears MR, Hancox RJ. Thumb-sucking, nail-biting, and atopic sensitization, asthma, and hay fever. Pediatrics 2016;138:e20160443. The hygiene hypothesis (biome diversity, biome depletion) accounts for many but not all of the environmental and other epigenetic factors that determine the risk of developing allergy. This study shows that the seemingly innocuous acts of nail-biting and thumbsucking are likely to contribute to protection against later allergic disease and is supportive of a Swedish study of hand versus machine dish washing that showed decreased allergic disease when dishes were hand-washed. In addition to the suggestion that there is oral exposure to an increased range of pro-inflammatory agents, the tolerogenic nature of dendritic cells in the oral cavity could also be promoting specific tolerance to ingested allergens (used in sublingualspecific immunotherapy). The authors avoided investigating food allergy and this is probably wise as self-reporting of food allergy is unreliable and there is a higher rate of false positive skin tests to food allergens than aeroallergens. It would be intriguing to see if thumb-sucking could offset the increase in food allergy associated with probable cutaneous introduction of foods via damaged skin in eczema. Fozia Roked, Jonathan North Birmingham Children’s Hospital, Birmingham, UK City Hospital, SWBH NHS Trust, Birmingham, UK Correspondence to Dr Fozia Roked, Birmingham Children’s Hospital, Steelhouse Lane, Birmingham B4 6NH, UK; fozia.roked@doctors.org.uk Contributors FR drafted the abstract/summary of original paper being picketed. JN drafted the commentary. Provenance and peer review Not commissioned; internally peer reviewed. REFERENCES 1 Hesselmar B, Hicke-Roberts A, Wennergren G. Allergy in children in hand versus machine dishwashing. Pediatrics 2015;135:e590–7. 2 Allam JP, Duan Y, Winter J, et al. Tolerogenic T cells, Th1/Th17 cytokines and TLR2/TLR4 expressing dendritic cells predominate the microenvironment within distinct oral mucosal sites. Allergy 2011;66:532–9. 3 Verrill L, Bruns R, Luccioli S, U.S. Food and Drug Administration. Prevalence of self-reported food allergy in U.S. adults: 2001, 2006, and 2010. Allergy Asthma Proc 2015;36:458–67. Table 1 Prevalence of atopy at age 13 years according to oral habit History of oral habits (%) No history of oral habits (%) p Value Atopic sensitisation/positive skin prick test (n=328) 38 49 0.009 Asthma (n=95) 13.3 12.8 0.8 Hay fever (n=219) 29.6 29.9 0.9 Table 2 Atopic sensitisation and type of oral habit Outcomes Thumb-sucking or nail–biting, OR (95% CI) Thumb–sucking, OR (95% CI) Nail-biting, OR (95% CI) Atopic sensitisation/positive skin prick test at 13 years (n=724) 0.64 (0.45 to 0.90) 0.64 ( 0.42 to 0.97) 0.70 (0.47 to 1.10) Atopic sensitisation/positive skin prick test at 32 years (n=935) 0.62 (0.45 to 0.86) 0.69 (0.47 to 1.00) 0.71 (0.49 to 1.02)