Third-hand smoke may affect growth of baby

The findings showed that the residue of the smoke puts babies and toddlers at much greater risk because they come into contact with contaminated surfaces while crawling or teething during their critical period of immune system development.

"We suspected the young are most vulnerable because of their immature immune systems, but we didn't have a lot of hard evidence to show that before," said lead author Bo Hang, scientist at Lawrence Berkeley National Laboratory (Berkeley Lab) in California, US.

Further, the dangers associated with smoking continues for a long time, even after the cigarette is snuffed out, the researchers said.

For the study, appearing in the journal Scientific Reports, the team studied the changes to body weight and the hematopoietic system after three weeks of exposure for two age groups of mice: birth to 3 weeks (neonatal) and 12-15 weeks (young adult). 

They were compared to a control group of mice that were not exposed to smoke.

The results revealed new-born mice exposed to smoke weighed significantly less than mice born in a control group. 

In addition, new-born and adult mice exposed to third-hand smoke showed persistent changes in blood cell counts. 

There were lower levels of platelets and specific types of white blood cells -- associated with inflammation and allergic reactions -- in the smoke-exposed mice. 

"The effects on blood cell count persisted even after exposure ended. Changes remained at least 14 weeks after exposure ended for the neonatal group and two weeks after it ended for the adults," Hang said.