Children who suck their thumbs and bite their nails suffer fewer allergies, study finds
Children who suck their thumbs and bite their fingernails are less likely to suffer from allergies later in life, a study has found.
The habits, which babies develop in the womb, protect youngsters from allergens including house dust mites, grass, mould and fur by exposing them to germs from an early age and altering their body’s immune functions.
They also help protect throughout adulthood, even if the children's parents suffered from allergies, or they grew up in a house with pets or people who smoke in it, the study added.
Prof Malcolm Sears, from McMaster University in Canada, said the findings are consistent with “hygiene theory”, which suggests that early exposure to microbes, or germs, reduces the risk of developing allergies.
He added: “While we don’t recommend that these habits should be encouraged, there does appear to be a positive side."
The study, led by the University of Otago in New Zealand and published in Pediatrics, following the progress of 1,037 participants from birth through to adulthood.
Parents reported their children's thumb-sucking and nail-biting habits when their children were aged five, seven, nine and 11.
The children were then tested for allergies using a positive skin prick test, with researchers testing at least one common allergen at ages 13 and 32.
Their findings showed children who sucked their thumbs or bit their nails had a lower prevalence of sensitisation at the age of 13 than those who did not - 38 per cent compared with 49 per cent. Those who displayed both habits had an even lower risk of 31 per cent.
This protection remained without throughout the participants' lives, with the level the same when the they were tested at 32.
Prof Bob Hancox, the lead author of the study, reiterated Prof Sears’ comments and said the findings “suggest that being exposed to microbes as a child reduces your risk of developing allergies”.
However, although thumb-suckers and nail-biters had fewer allergies on skin testing, the study found no difference in their risk of developing allergic diseases such as asthma or hay fever.