Scientists have figured out why children with asthma are less likely to respond to treatment for the condition if they are exposed to passive smoking at home.

Currently in Ireland, one in every five children has asthma.

According to UK researchers, it is already known that passive smoking can lead to a worsening of asthma symptoms. It also impairs a child's response to inhaled steroid treatment. However until now, the reason for this was not known.

The researchers from Imperial College London have discovered that children exposed to secondhand smoke at home have lower levels of the enzyme, HDAC2, compared with children who live in non-smoking homes.

When it comes to asthma, this enzyme is necessary to allow steroids to exert their anti-inflammatory effects.

In other words, children with lower levels of HDAC2 are ‘less sensitive to inhaled steroid treatment, so they suffer more symptoms and might have to take higher doses of steroids, which may lead to side-effects', noted Prof Peter Barnes of Imperial College London.

"These findings underline the importance of legislation aimed at protecting children from being exposed to cigarette smoke," he said.

The study involved 19 children with severe asthma, nine of whom lived in homes where their parents smoked.

It found that children living in ‘smoking' homes had about half the levels of HDAC2 compared to the children living in non-smoking homes.

"Children with asthma who are passively exposed to cigarette smoke have the same molecular abnormalities that lead to steroid resistance as adults who actively smoke. The mechanism we've identified will be a target for new treatments to help children with severe asthma," Professor Barnes added.

Details of these findings are published in the journal Chest.

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