This is because they would breathe in the black coal dust and over many years more and more accumulates in their lungs and their lungs become blacker.
Each stick heats rather than burns the tobacco at around 240-280C and delivers roughly 4 minutes or 13 draws per session
Home detox safety checklist: regular check-ins, emergency numbers handy, stay hydrated, avoid driving, remove substances, have comfort items ready
The downstream effects of state tobacco control policies on maternal smoking during pregnancy and birth outcomes
Nonsmokers' Perceptions of Cigarette Smokers' Credibility, Likeability, Attractiveness, Considerateness, Cleanliness, and Healthiness. Communication Research Reports 27 (2): 14358