Research: Children who suck their thumb cut their risk of developing an allergy

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.