Personally, as a wild guess, I would consider chlorine gas from the growing use of showers as a cancer-causative factor. With US Prohibition history, the Tobacco industry will pale compared to the Anti-Tobacco industry. His predictions materialized. Today, the politicization of a personal choice is fraught with political symbolism. Cigarettes are bad for women, cause every ill, must be banned from homes, and are now grounds to remove custody of children.
Smokers band pathetically, fighting the inevitable.
Total rest and quiet cause adverse symptoms. Though history we've lived in high-smoke environments. Smoke-filled huts sheltered us from brush fire haze. The starting point should be we're actually adapted to a level of smoke. No baseline comparison exists.