Young children and babies exposed to second-hand smoke have levels of a nicotine by-product in their bodies comparable to an adult smoker, a new study has found.
Sixty-three percent of children aged up to four tested in the Pennsylvania State University study tested positive for traces of cotinine, which is produced when the body breaks down nicotine.
Shockingly, 15 percent of children had cotinine levels only normally seen in adult smokers.
"It was definitely more than we expected, and it's scary," said Lisa Gatzke-Kopp, lead author and a professor of human development and family studies at Pennsylvania State University.
"Smoke continues on in the environment even after the cigarette is out."
According to the New Zealand Health Promotion Agency, children exposed to second-hand smoke are twice as likely to develop bronchitis and pneumonia, and it can also cause glue ear and meningitis, make asthma worse, hamper lung growth and SUDI (Sudden Unexpected Death in Infancy).
A recent Massey University study estimated around 100 people in New Zealand die every year due to exposure from second-hand smoke.
Researchers believe young children are more at risk from second-hand smoke because they breathe faster than older children and touch more things.
"I think some parents are trying to reduce their children's exposure," said Prof Gatzke-Kopp. "They're making a good effort. They go outside, or they don't smoke around their child, but they may not know it's all over them, and when they pick the baby up and cuddle the baby, the baby's getting it through their clothes, their hair...
"Because infants often put objects into their mouths and crawl on floors, they may be more likely to ingest smoke residue or get it on their skin, compared to older children."
Most of the mothers claimed not to be smokers at all - 70 percent - but 25 percent admitted smoking throughout their pregnancy.
The children mostly came from rural low-income backgrounds, with levels of cotinine correlating with poverty. Children who spent their days in daycare - and presumably away from second-hand smoke - generally had lower levels of cotinine.
But don't think it's just a rural issue - it's suspected city kids are at even more risk.
"It might be even more worrisome, in that kids in urban environments are operating in more of a toxic chemical soup than kids in a more rural environment," said Clancy Blair, senior author and professor of cognitive psychology at New York University.
Their next step is to see if the increased cotinine levels have an effect on the children's development and health.
"It's definitely true that nicotine binds in the brain in special receptors that affect things like cognition and attention, and there's every reason to believe all brains are equally vulnerable," said Prof Gatzke-Kopp.
Labour, the majority partner in the coalition Government, is presently considering new legislation that would ban smoking in cars. MP Louisa Wall says banning smoking in the home could come after that.
The latest research was published in journal Nicotine & Tobacco Research.