Children that suck their thumbs and bite their fingernails may suffer fewer allergies as adults, finds study

Child Thumbs Up

Thumb-sucking children and children who bite their fingernails could be less likely to develop allergies – supporting what has been dubbed the “hygiene theory” – according to a new study carried out by the University of Otago in New Zealand.

The findings, published in the US journal Pediatrics, emerged from the Dunedin Multidisciplinary Study, which tracked the progress of 1,037 participants born in the early 1970s throughout their childhood and on into adulthood. The results suggest that early exposure to microbial organisms – common culprits that trigger allergies in many people, such as house dust, pet hair, grass and mould spores – via the hand to mouth transfer associated with thumb-sucking and fingernail biting may reduce the risk of developing such allergies. The researchers suggest that such childhood behaviours could also have a beneficial protective effect on the immune system which may continue into later life.

Child Playing Beach

Exposure “may alter immune function”

Lead author of the study, Professor Bob Hancox says this exposure “may alter immune function” as it develops in these children, making them less prone to developing allergic reactions to common allergens. The parents of the children who took part in the study were asked to report thumb-sucking and nailbiting behaviours at two-yearly intervals between the ages of five and 11, with checks for atopic sensitisation – a skin prick test – carried out at the ages of 13 and again at age 32. The first round of atopic sensitisation tests revealed that children who bit their fingernails were 11% less likely to have a positive sensitisation result, and children who engaged in both behaviours were 18% less likely to prove positive for allergies, compared with children who did not engage in either habit.

Child Playing with Cat

“Hygiene theory”

Professor Hancox says that he and his colleagues are not suggesting that children should be encouraged to take up such habits, since any true health benefit remains unclear as yet.

However, Professor Malcolm Sears of McMaster University in Canada says the findings are consistent with “hygiene theory”, which maintains that early exposure to microbes may reduce the incidence of allergies – which are on the increase globally, particularly amongst children. He says: “While we don’t recommend that these habits should be encouraged, there does seem to be a positive side.”

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