Parents who smoke are being warned to stop as they could be making you sick.
A top children's hospital in Liverpool says up to one in three kids treated for certain conditions, are ill because their parents smoke in front of them.
Conditions like bronchitis, asthma and ear infections can be caused or made worse by breathing in cigarette smoke.
Now Doctors at Alder Hey Hospital say the number of kids with these conditions could be really reduced if people stopped smoking around them.
Dr Steve Ryan said of the 35,000 children treated by the hospital every year, 2,000 were there because they'd been exposed to their parents' smoke.
He agreed that it was hard for some people to give up smoking, but said there were still things they could do to protect you.
One idea is for smokers to put on another layer of clothes when they smoke outside, so that when they come indoors they can take it off and their clothes won't be so smoky.