New research indicates that exposure to third-hand smoke leads to biological effects on weight and blood-cell development that could be damaging to one's health.
This type of smoke refers to residual nicotine and other chemicals from tobacco smoke that lingers on indoor surfaces such as furniture and carpets.
The study, led by researchers from the US Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), provided evidence that newborn mice housed with smoke-treated cloths for three weeks weighed significantly less than mice in a control group.
Reporting their findings in a paper in Scientific Reports last Friday, the Berkeley Lab team and researchers from the University of California, San Francisco, and Nanjing Medical University in China found that newborn and adult mice exposed to third-hand smoke had persistent changes in blood-cell counts associated with the immune system.
The blood-cell count changes are associated with inflammatory and allergic reactions upon exposure to third-hand smoke.
"We suspected that the young are most vulnerable because of their immature immune systems, but we didn't have a lot of hard evidence before," said study lead author Bo Hang, a Berkeley Lab staff scientist who previously found that third-hand smoke could lead to genetic mutations in human cells.
He added: "In this case, we found that third-hand smoke appeared to inhibit weight gain in neonatal mice, but not in the young adults."
While the effects on weight were seen only in neonatal mice, changes in blood-cell populations were evident in both age groups.
In general, there were higher levels of platelets and specific types of white blood cells in the smoke-exposed mice.
For example, neonatal mice exposed to third-hand smoke had higher levels of eosinophils, female adults had higher levels of neutrophils, male adults had higher levels of basophils and all the mice had higher levels of B cells.
"Those are all types of white blood cells associated with inflammation and allergic reactions," said co-author Jian-Hua Mao, who is also a Berkeley Lab scientist.
"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."
The weight effect was temporary for the mice as they caught up with their non-exposed peers in weight weeks after the exposure to smoke stopped.
The researchers acknowledged that they did not study whether the biological changes led to specific diseases or other health outcomes, but said that human babies and toddlers are at greater risk as they come into contact with contaminated surfaces while crawling or teething during a critical window in the development of their immune system.