well... they won t if you keep smoking even 2-3 a day. many many effects ... let us start with the worst a 25% incidence the baby will develop a lung condition if the parent smokes. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1745164/ (odds ratio = times more likely... 1.1 to 1.3 x more likely ... 25% but all the textbooks say that). circulation risk and increased risk of heart problems ..probably doubles. A few cigarettes still carries most of the risk. Stopping and the circulation changes in days to a few weeks back to a non-smoker. Lung damage.. 2-3 cigarettes is better than living in Beijing (seriously). but there is a (small) increased amount of damage to the lungs from 2-3 cigarettes. In theory if one stops the lungs start to heal up and improve for 1-2 years but only if one stops. There is clearance of gunk in the lungs too if one stops. If one has asthma, then stopping improves lung function markedly and more rapidly (weeks to months rather than years). Lung cancer is proportional to number of cigarettes and at 2-3 cigarettes the risk is not huge but is measureably worse. Stopping lowers risk and it goes back to that of a non-smoker in about 10 years of totally quitting.