Smoking far outweighs all other factors, including air pollution and occupational exposures, in causing these conditions. Persons with these conditions often suffer long periods of disability marked by progressive shortness of breath and limitations on many daily activities. Smoking has an adverse effect on the body's immune system and other defense mechanisms. The risk of respiratory infections, such as pneumonia and influenza, is increased in smokers compared to nonsmokers. A recent study concluded that smoking increases susceptibility to the common cold.
Smoking has a direct effect on the growth of the fetus.
The more the mother smokes during pregnancy, the lower the weight of the newborn infant. Smoking appears to both decrease the quantity of breast milk and change its quality, and may lead to early weaning. Women who smoke during pregnancy incur extra risks to their own health, as well as to that of the fetus. Abnormalities of the placenta and bleeding during pregnancy are increased with smoking, and the more a pregnant woman smokes, the greater the risks. When ulcers are present, they heal less readily in smokers and are more likely to recur.