FCAAIA Notes: I only posted this article because I thought the idea of the study was an interesting concept.  I think the results fall into the “You never really know, do you?” category.  Although children with oral habits as infants and toddlers were less likely to have positive skin tests at 13 years old, they were not less likely to have clinical symptoms of allergy.  However, at age 32, they were less likely to have allergy. Does that mean that over time their positive skin tests became less clinically relevant?  Or are the statistics an artifact because only 70% of 13 year olds had skin testing?

ALL infants and toddlers have oral habits, don’t they?  Aren’t they ALWAYS exploring their environment by putting things in their mouths? The best answer as to whether oral habits early in life would come in the form of a prospective study.

As far as thumb sucking goes, I’ll leave you to discuss orthodontic risks with your dentist.

(Source:  July 12, 2016)

Children who sucked their thumbs or bit their nails were associated with a statistically significant reduced risk of developing allergies as adults, according to another study that appeared to support the “hygiene hypothesis.”

Young children with at least one “oral habit” (thumb-sucking, nail-biting or both) were associated with a 39% reduced risk of developing atopic sensitization, or common allergies at age 32 (OR 0.61, 95% CI 0.46-0.81, P=0.001), reported Stephanie J. Lynch, of University of Otago in Dunedin, New Zealand, and colleagues.

However, there was no significant association between children with at least one oral habit and the likelihood of developing allergies at age 13 (OR 0.67, 95% CI 0.48-0.92, P=0.13), the authors wrote in Pediatrics.

Explaining the hygiene hypothesis, Jay Portnoy, MD, of Children’s Mercy in Kansas City, Missouri said “Children with such habits are known to ingest bacteria that are on their hands and this is believed to protect them from developing allergies later in life.”

“It is possible that other factors may have played a role, but the investigators controlled for as many factors as they could think of and this did not change the results,” Portnoy, who was not involved with the study, told MedPage Today via email.

The association between oral habits and reduced risk of allergies appeared to be most pronounced later in life. Even after adjusting for confounders, the relationship between thumb-sucking and nail-biting and a decreased risk of allergies remained significant.

Lynch and colleagues examined the association between specific allergens, including house dust mite, cat and grass, and risk of later allergies, and found similar results. The associations between oral habits in young children and allergies as adults were significant, but the associations between oral habits and allergies in teenagers were not.

But not surprisingly, atopic sensitization was lower among 13-year-olds who had an oral habit as children versus those who did not (38% versus 49%, P=0.009) and was lowest among teenagers who had previously both sucked their thumbs and bit their nails at one point in time (31%, P=0.05).

Further, there was no significant association between the development of asthma (13.3% versus 12.8%, respectively, P=0.8) or hay fever (29.6% versus 29.9%, respectively, P=0.9) in children who did have oral habits compared to those who did not.

Co-author Robert J. Hancock, MD, also of University of Otago, said that while the findings support the idea that exposure to microbial organisms influences the immune system and makes one less likely to develop allergies, the actual implication of these findings for patients and their parents is not yet known.

“Many parents discourage these habits and we do not have enough evidence to change this,” Hancox said in an email to MedPage Today. “We certainly don’t recommend encouraging nail-biting or thumb-sucking, but perhaps if a child has one of these habits and is difficult to stop, there is some consolation in the knowledge that it might reduce their risk of allergies.”

Researchers examined a cohort from the Dunedin Multidisciplinary Health and Development, a population-based birth cohort study, with follow-up from ages 3 years to 38 years. At ages 5, 7, 9, and 11 years, parents were asked about a child’s oral habits. This was followed up with a skin-prick test at age 13 and 32.

Overall, of the 1,013 participants, 317 (31%) had at least one oral habit, and 328 out of 713 (45%) showed atopic sensitization at age 13.

Limitations to the study include the fact that oral habits were based on parental reports, that the children may have developed atopic sensitization before information about their oral habits was gathered, as well as the fact that only 70% of 13-year-olds consented to skin-prick tests.

Hancox said that understanding why people have allergic diseases is important, and that this research appears to support the hygiene hypothesis as a potential explanation.

“The hygiene hypothesis is one explanation for the rising prevalence of allergies over recent decades and it is important to know whether this true,” said Hancox. “I don’t think that we know enough to suggest that pediatricians alter their practice or advice to parents yet.”

Portnoy also seemed to feel that the topic needed more research, adding “Of course further studies may provide more detailed information about this, so stay tuned.”

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