If I smoke, should I breastfeed?
Breast milk is the best food for infants, regardless of whether a mother smokes. However, for the same reasons it is recommended that pregnant women do not smoke, breastfeeding mothers should not smoke because nicotine, thiocyanate, and other toxicants are transferred through the human milk to the infant.
Another reason not to smoke and breastfeed is that infants of women who smoke are weaned at an earlier age. If a mother does continue to smoke, she should never breastfeed while smoking, because a high concentration of smoke will be in close proximity to the infant. It is also advised not to smoke immediately before breastfeeding.
Source: Pediatric Environmental Health, 3rd Edition (Copyright © American Academy of Pediatrics 2011)