There’s no “safe” number of cigarettes to smoke per day, as any amount increases your cancer risk. A 2021 study of 229,028 Australians found that by age 80, only 1% of non-smokers developed lung cancer, compared to 14% of smokers.
Smoking 1–5 cigarettes daily raises the risk to 7.7%, while smoking over 35 increases it to 26.4%. Secondhand smoke also significantly increases lung cancer risk.