It's a dilemma faced by millions of parents worldwide – how to stop their children sucking their thumb.
But researchers have found that the habit may bring unexpected health benefits – and the same is true for nail biting.
Scientists
have discovered that children who sucked their thumbs or bit their
nails were more than a fifth less likely to have allergies as adults.
And if they did both bad habits, the risk was slashed by more than a third.
Researchers
believe these children ingested the bacteria living under their nails
which strengthened their immune system, making them less susceptible to
allergies.
This
is known as the ‘hygiene hypothesis’ – and is also a possible
explanation as to why allergies are commoner now than during Victorian
era when sanitation was far worse.
But
despite their findings, they would not want parents to actively
encourage their children to thumb suck or bite nails as there can be
other health risks.
They tend to be more susceptible to picking up tummy bugs and thumb sucking may pull the front teeth forward.
And there is no evidence from this study that the habits reduce the risk of asthma or hayfever, one of the commonest allergies.
But the
discovery may help allay parents’ fears if they are really struggling to
wean children off the habits, according to the team from the University
of Otaga in New Zealand.
Estimates show that around 50 per cent of children suck their thumbs or two fingers and another 30 per cent bite their nails.
Professor
Bob Hancox looked at the records of 1,037 women and men who have been
followed since they were children in the early 1990s as part of a major
New Zealand health study.
All had undergone finger prick tests to check if they had any allergies aged 13, and again at 32.
On
average, 49 per cent had at least one allergy aged 13 or 32 but this
was slashed to 38 per cent if they bit their nails or sucked thumbs.
If
they did both, the risk of having an allergy was cut to just 31 cent,
according to the findings published in the journal Pediatrics.
Professor
Hancox said: ‘The findings support the “hygiene hypothesis”, which
suggests that being exposed to microbes reduces your risk of developing
allergies.
Stephanie
Lynch, a medical student who was also involved in the project said:
‘They ingest the bacteria living under their nails and as it goes
through it may influence the immune system into working in a different
way.
‘That builds an immune response, making them less susceptible to allergies.’
‘I
wouldn’t tell children to go out and suck their thumbs but it may just
give a little peace of mind to parents and take the stress out.’
Most children suck their thumbs from the ages of 3 to 6 to sooth themselves, or sometimes because they are bored.
If
they continue much older when their adult teeth start to come through,
they can push the front ones forward so they are wrongly aligned.
