Healthy children are considered to be a sensitive group for ozone and particle pollution. This is because children are usually more active outdoors than adults, and they breathe more air per pound of body weight, so their exposure to air pollution is greater than adults. In addition, their lungs are still developing. It's variable, but most children's lungs don't finish developing until they finish growing, usually around the age of 18. Studies indicate that air pollution can affect this development. Also, children are more likely than adults to have asthma, which can be aggravated by air pollution. This may lead to health impacts such as increased medication use and increased visits to health care providers, including emergency rooms.