Kids Who Bite Their Nails And Suck Their Thumbs Develop Fewer Allergies

Parents, you can stop fretting about your child's disgusting habits. An analysis of more than 1000 kids between the ages of five and 11 reveals that nail-biters and thumb-suckers are less likely to develop allergic sensitivities later on in life. Image: Shutterstock

New research published in the journal Pediatrics shows that children with these habits are less likely to develop allergies to house dust mites, grass, cats, dogs or airborne fungi. It's further evidence in support of the so-called "hygiene hypothesis", which suggests that childhood exposure to microbial organisms and other nasties alters immune function, resulting in a decreased risk of developing allergies.

"While we don't recommend that these habits should be encouraged, there does appear to be a positive side to these habits," study co-author Malcolm Sears of McMaster University said in a statement.

For the study, the researchers took data from the ongoing Dunedin Multidisciplinary Study, which is following the progress of 1037 participants born in Dunedin, New Zealand from 1972 to 1973. Back when this study got started, parents reported their children's thumb-sucking and nail-biting habits when they were five, seven, nine and 11 years old. When these children turned 13, and again at 32, they were checked for atopic sensitisation -- a skin prick test that detects a sensitivity to at least one common allergen.

Slightly less than a third of all children enrolled in the study were frequent nail biters or thumb suckers. By the time these kids reached their teenage years, nearly half showed an atopic sensitisation of some sort -- so oral habit or not, half of these kids still developed an allergy. But for those with one oral habit, their chance of developing an allergy dropped to 40 per cent. And for those with both habits, this figure plummeted to 31 per cent. That's significant.

This trend held true into adulthood, and was not altered by factors such as smoking in the household, owning cats or dogs, exposure to house dust mites or breastfeeding. And this study did not find associations between nail-biting and thumb-sucking with the onset of asthma or hay fever.

Oral habits such as thumb-sucking and nail-biting are likely providing a channel through which microbial organisms can enter the body, particularly at a young age. But it would be a mistake to deliberately expose our children to these pathogens, which could lead to sickness. Moreover, the authors of the new study aren't suggesting that children be encouraged to take up these habits, saying there's no clear-cut evidence of a true health benefit.

Relatedly, previous studies have shown that most peanut allergies can be staved off by not withholding peanuts from children before the age of three. This makes sense when you think about it. An allergic reaction is basically the body's immune system freaking out when it detects a potentially dangerous foreign agent. By "training" the immune system at a young age to recognise certain substances as being harmless -- whether they be benign microbes or peanut particles -- we may be able to reduce our chances of developing an allergy in the future.


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    Yes, but what about kids who play Pokémon Go? How does their allergy development compare?

    It makes sense right? Expose your body to these things and you will build a natural immunity ,etc. I've been biting my nails my entire life... Never had:
    Flu (firing both ends kind, you know the actual flu)
    My last cold (snotty nose, cough ,etc) was 3 years ago.

      Chickenpox, Measles, etc aren't the same as allergies. You are right in that sucking your thumb will build up your immune system. It's a lot less effective than getting vaccinations but it will still help.

      Allergies are another thing. An allergy is an over active immune system. Your body treats something as a huge threat and over reacts. Allergies develop in two ways. First is non-exposure. In this case it makes some sense. If you pat a cat then suck your thumb you're providing exposure to the cat and are less likely to develop a cat allergy. But the second method of development is over-exposure or sympathetic exposure. If you have too much exposure to something that already triggers an immune response then eventually you'll develop an allergy to it. This is how bee sting allergies develop.

      Sympathetic exposure is when you get sick while also being exposed to an allergen. This way the allergen becomes a trigger for immune response. If you ingest chemicals from cat hair follicles that also carry harmful bacteria then later in life any exposure to cat hair may trigger an allergic response even if the harmful bacteria are no longer present.

      Has nothing to do with "natural immunity". Try exposure. Have a child, place them in child care, kiss your child when it gets sick. Tell me how immaculate your immune system.

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