Nicotine from clothes, furniture and walls, or breath of smokers may contribute to the observed levels

Study authors

The findings were part of a study looking at children admitted to hospital with respiratory illness - and examining the effects of environmental tobacco smoke on their health.

A total of 322 children aged between three and 27 months provided samples, and questionnaires were used to compare the results with the actual smoking habits of their parents at home.

Accurate test

They found the hair nicotine levels were able to more accurately discriminate between the smokiest homes and those where parents did not smoke, or only smoked outside the home.

One of the more surprising results they found was that even parents who only smoked outside the home still had children with nicotine in their bodies.

The level of nicotine was halfway between children in a complete non-smoking household, and the level in a house of smoking adults.

The authors of the study, from the Wellington School of Medicine in New Zealand, said: "Nicotine from clothes, furniture and walls, or breath of smokers may contribute to the observed levels.

Three million adults are exposed in their workplaces

Action on Smoking and Health

"Another explanation is that the caregivers in this study were not reporting accurately about their smoking habits."

Clive Bates, a director of Action on Smoking and Health (ASH), an anti-smoking campaign group, said that should hair sampling prove an accurate way of testing for nicotine levels, it could prove useful for health and safety examinations of workplaces.

He said: "Reliable studies have said that very serious diseases such as lung cancer can be caused by passive smoking."

He added: "Three million adults are exposed in their workplaces."