Thumb Sucking and Nail-Biting Decrease Allergy Risk

sucking thumb and nail biting decrease risk of allergies

Thumb sucking reduces allergy risk

Thumb sucking and nail-biting after the age of three is often frowned upon by parents. Embarrassed parents will often apply awful-tasting ointments on a child’s thumb and fingers to prevent thumb sucking or nail biting. And for many years after, former thumb-suckers and nail-biters can face embarrassment when parents bring up their former childhood habit.

Well, later thumb suckers and nail biters now have something to be thankful for. Turns out that thumb sucking and nail biting actually decreases a child’s risk of allergies later on – even into adulthood.

Why? As we’ll discuss below, it has to do with microbes and immunity. First, let’s gather some of the facts.

How many children bite their nails or suck their thumbs?

Studies have found that a majority of children will suck their thumb by the age of three years old. A 2016 study from Italy on 235 kids found that 74 percent of kids at age three were sucking their thumbs.

But this goes way down after the age of three. A study from India on over 800 children found that nearly nine percent of children between age six and 12 still sucked their thumbs. And almost 6 percent were biting their nails.

Allergies inhibited by thumb-sucking/nail-biting

Researchers from New Zealand’s Dunedin School of Medicine have been following 1,037 residents of Dunedin, New Zealand for over two decades as part of the Dunedin Multidisciplinary Health and Development Study.

The study subjects were all born between 1972 and 1973. About a third of the children (31 percent) sucked their thumbs or bit their nails between the ages of five and 11 years old.

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So we’re not talking about the effects of sucking thumbs or biting nails under the age of five. Rather, the research focused upon those children who persist in thumb-sucking and/or nail-biting for years after.

The children were given assessments every 2-3 years starting at the age of 3 and up to the age of 38. At the age of 13, the researchers began testing the children for allergies using skin-prick testing. Skin-prick testing is still the current standard for confirming a definite allergy.

The researchers also tested the subjects for allergies at the age of 32 years old.

Testing was done for the following allergies:

• dust mite allergies
• grass allergies
• dander allergies to cats, dogs and horses
• allergies to kapok
• allergies to wool
• allergies to Aspergillus
• allergies to Alernaria
• allergies to Penicillium
• allergies to cockroaches

Nearly half (46 percent) of the children had one of these allergies at the age of 13 years old. The most prevalent allergies were grass pollen, house dust mites and cat dander.

The researchers found that allergies were decreased by nearly 40 percent (37 percent) in children who sucked their thumbs or bit their nails between five and 11 years old. And by the age of 32, older thumb-suckers or nail-biters also had nearly 40 percent (39 percent) fewer allergies.

And those children who sucked their thumbs and bit their nails had even a lower incidence of allergies.

In terms of allergy percentages, at the age of 13, 49 percent of those who didn’t suck thumbs or bite nails had allergies. In comparison, less than 39 percent of those who sucked their thumbs had an allergy. And only 31 percent of those who sucked thumbs and bit nails had an allergy.

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Why does thumb sucking and nail biting decrease allergies?

The issue relates to the immune system becoming stronger with greater exposures during childhood. Children who have greater exposure to bacteria, viruses and the various allergens that are floating around will tend to have stronger immune systems.

This is reflected by their sensitivities to allergies. It is also linked with the development of strong colonies of probiotics among children. Other studies have shown that probiotics discourage allergies and hay fever.

Dr. Malcolm Sears, who has been the senior researcher of this study from his days at Dunedin University School of Medicine, is now a professor of medicine at McMaster University School of Medicine. Dr. Sears confirms the connection between the immune system and what is called the hygiene theory:

“Our findings are consistent with the hygiene theory that early exposure to dirt or germs reduces the risk of developing allergies.”

Should parents let their kids suck their thumbs or bite their nails later?

The answer to this question would depend upon each individual situation. If the child’s habits are causing other issues, then a consult with a health professional is probably a good call. Dr. Sears also commented on this point:

“While we don’t recommend that these habits should be encouraged, there does appear to be a positive side to these habits.”

For example, in the Italian study mentioned above, 18 percent of the children by the age of three had anterior open bite occurrence. In a 2011 study from Brazil, 40 percent of kids between 30 and 59 months sucked their thumbs, and anterior open bite was found in 30 percent of the children.

What is anterior open bite?

Anterior open bite is when the teeth do not close correctly on the front teeth. There should be a small overlap between the top and the bottom teeth. They should also come down completely into this overlap when the back teeth are brought together.

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When the back teeth are brought together and there is still a space between the top and the bottom teeth in the front, this is called anterior open bite.

Anterior open bite might be genetic, but it also may be caused by thumb sucking. This is because the thumb will be pressed into the top gums, causing those teeth to come out at an angle.

To a lesser degree, anterior open bit may be caused by a constant chewing on objects. This may include nail biting. Anterior open bite may also be encouraged by what is called tongue thrusting.

Hygiene conclusion

The bottom line is that kids should be allowed to roam around their environments and around nature. Antibiotics, antibacterial soaps and other hygiene strategies may interfere with a child’s development of strong colonies of probiotics.

Learn other ways to beat allergies and hay fever:

hay fever folded side



Lynch SL, Sears MR, Hancox RJ. Thumb-Sucking, Nail-Biting, and Atopic Sensitization, Asthma, and Hay Fever. Pediatrics. Published online July 11 2016

McMaster University Release. Thumb-sucking and nail-biting have a positive side. July 11, 2016.

Garde JB, Suryavanshi RK, Jawale BA, Deshmukh V, Dadhe DP, Suryavanshi MK. An epidemiological study to know the prevalence of deleterious oral habits among 6 to 12 year old children. J Int Oral Health. 2014 Feb;6(1):39-43.

Silvestrini-Biavati A, Salamone S, Silvestrini-Biavati F, Agostino P, Ugolini A. Anterior open-bite and sucking habits in Italian preschool children. Eur J Paediatr Dent. 2016 Mar;17(1):43-6.

Vasconcelos FM, Massoni AC, Heimer MV, Ferreira AM, Katz CR, Rosenblatt A. Non-nutritive sucking habits, anterior open bite and associated factors in Brazilian children aged 30-59 months. Braz Dent J. 2011;22(2):140-5.

Case Adams, PhD

Case Adams has a Ph.D. in Natural Health Sciences, is a California Naturopath and is Board Certified as an Alternative Medicine Practitioner, with clinical experience and diplomas in Aromatherapy, Bach Flower Remedies, Blood Chemistry, Clinical Nutritional Counseling, Homeopathy and Colon Hydrotherapy. He has authored 27 books and numerous articles on print and online magazines. Contact: [email protected]

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