Sucking thumbs in children is a protective mechanism against allergies

Sucking the thumb can protect against allergies
Children are actually told not to suck their thumbs or chew their fingernails. However, researchers have now found that so-called thumb sucking and chewing fingernails means that those affected later in life are less likely to have certain allergies.

Children like to suck on their thumbs and chew on their fingernails. They usually hear from their parents that they should stop. However, scientists from the University of Otago and McMaster University have now found that sucking your thumb and chewing your fingernails can prevent you from developing certain allergies in later life. The doctors published the results of their study in the specialist journal "Pediatrics".

Early exposure to dirt and germs reduces risk of allergies
Sucking thumbs and chewing fingernails are habits that babies develop in the womb. This protects them as adolescents from various allergens, say the doctors. These include, for example, dust mites, grass, mold and animal hair. When children are exposed to such germs, their body's immune functions change. Our results are consistent with the hygiene theory that early exposure to dirt and germs reduces the risk of developing allergies, explains author Professor Malcolm Sears.

Childhood habits also help us in adulthood
The "negative" habits from childhood also help us in adulthood. Even if children already had allergies and grew up in a house where there were pets or parents smoked, the experts say. Of course, we don't recommend that children should be encouraged to do this now, but there does seem to be a positive side, says Professor Sears of McMaster University in Canada.

Doctors observe subjects from birth to the age of 32
The new study was carried out by the University of Otago in New Zealand and McMaster University in Canada. The scientists examined 1,037 participants from birth to adulthood. The parents of the children reported habits such as thumb sucking and nail biting at the age of five, seven, nine and finally at the age of eleven. Tests for a common allergen were carried out between the ages of 13 and 32, the experts say. The doctors used a so-called prick test. With the help of this skin test, the suspicion of an increased readiness for allergies can be confirmed or sensitization excluded.

Protective effect found in 13 year old children
The results of the study show that children who sucked the thumb or chewed their fingernails had fewer allergies at the age of 13 compared to children who hardly sucked the thumb. 38 percent of the thumb suckers suffered from allergies, compared to 49 percent from the control group. If children had done both habits regularly, their risk dropped to 31 percent, the authors say.

Allergy risk in later life decreases when children are exposed to different microbes
This protective effect was retained even when the test subjects were already 32 years old. The protective effect was still at the same level at this age, the experts explain. The new results suggest that our risk of allergies later in life decreases when we are exposed to various microbes as a child, says lead author Prof Bob Hancox.

No benefit found in risk of asthma and hay fever
But even if thumb sucking and nail biting resulted in fewer allergies in the skin tests performed, no difference in the risk of allergic diseases such as asthma or hay fever could be determined, the scientists add. (as)

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