thumb sucking bolsters the decades-old,
controversial “hygiene hypothesis,” which
claims that exposure to some bacteria early in
life could improve health down the road.
The latest results come from the Dunedin
Multidisciplinary Study , which has followed
more than 1,000 people in New Zealand over
four decades. Researchers from the University
of Otago used the data to see if thumb-
sucking and nail biting, both common
childhood behaviors, were correlated with
lower rates of allergic reactions later in life.
Not Such a Bad Habit
After sifting through the data, the researchers
found limited evidence to support the hygiene
hypothesis. For the study, parents were asked
to report thumb-sucking and nail-biting
behaviors when children were between 5 and
11 years old, and the participants were tested
for allergies via a skin test when they were 13
and 32.
Researchers looked at a range of common
allergies including dust mites, grass, cat and
dog dander, molds and more — they didn’t
test for asthma or hay fever. After controlling
for factors such as sex, pets, parental
allergies, breastfeeding, inveterate thumb-
suckers turned out to have fewer allergies.
However, the correlation wasn’t
overwhelming: They study found that 38
percent of children who sucked their thumb
or bit their nails had a skin reaction,
compared with 49 percent who didn’t.
Further, the cohort study relied on subjective
observations from parents who tracked hand-
to-mouth habits at home.
In other words, thumb-sucking is only a piece
of the puzzle here, and researchers still
couldn’t identify the mechanism to explain
why fingers in your mouth could prove to be
beneficial. Less than identifying thumb
sucking as a disease-fighting panacea, the
researchers underline the impact the impact
childhood behaviors have later in life. They
published their work Monday in the
journal Pediatrics.
How Clean Should We Be?
According to the hygiene hypothesis,
proposed in 1989 , the increased rates of
allergies and autoimmune diseases in
developed countries can be explained by our
obsession with cleanliness. As the thinking
goes, the immune system can be “trained”
with small doses of a relevant pathogen so it
can learn how to launch a defense — the
more microbial introductions, the better. Still,
it remains a controversial and unproven
theory, with many questions still to be
answered.
Several epidemiological studies suggest that
kids who grow up on farms are protected
from asthma and hay fever. Sharing a
bedroom as a child, or growing up with
siblings could also bolster the immune system .
But for the many studies supporting the
hygiene hypothesis, there are just as many
that fail to find evidence that that “less
hygienic” behaviors provide a direct,
protective effect. Some scientists have even
proposed removing “hygiene” from the title
to focus more attention on the health impacts
of microbes, rather
than endorsing unhygienic behavior .
Other proposed methods to firm up our
children’s immune systems
include breastfeeding, natural births, outside
play and other allegedly “natural” behaviors.
The rise in antibiotic use has been pinpointed
as a factor as well, as courses of antibiotics
kill off both good and bad bacteria in our
bodies, and can affect our microbiome for up
to a year .
In all likelihood, exposure to bacteria via
dirty fingers is only one of a confluence of
factors regulating how our immune system
behaves later in life. The authors seem to
agree, stopping well short of suggesting a
daily regimen of thumb sucking for young
children. Rather, it seems thumb sucking may
not be the dirty habit that it’s often assumed
to be.
Source: Discover magazine
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