WEDNESDAY, March 30 (HealthDay News) -- Levels of nicotine in the hair of infants who sleep in the same room with parents who smoke are three times higher than in babies who sleep in another room, a new study finds.

The nicotine is from cigarette smoke particles that impregnate the parents' skin, clothes and hair, which is known as "thirdhand smoke," the Spanish researchers explained.

The investigators analyzed hair samples from 252 babies younger than 18 months and interviewed their parents about their smoking habits. Seventy-three percent of the parents said they smoked or allowed smoking in their homes, and 83 percent of the babies' hair samples showed high levels of nicotine.

The study also found that cigarette smoke toxins are still present in homes even when parents try to take action to protect their children's health, such as smoking by a window, ventilating bedrooms after smoking, or smoking when the baby is in a different room or not in the house.

"Passive smoking is the leading preventable cause of childhood death in developed countries," lead author Guadalupe Ortega said in a Plataforma SINC news release.

The study is published in the journal BMC Public Health.

More information

The U.S. Centers for Disease Control and Prevention explains how secondhand smoke harms children.