Health Risks
Chronic exposure to nicotine may cause the following:

coronary artery disease
peptic ulcer disease
reproductive disturbances
esophageal reflux
hypertension
fetal illness and death
delayed wound healing
Tobacco contains tar (numerous chemicals that cause a thick, sticky substance when smoked), about 2000 chemicals total.  Tobacco and various components have been associated with an increase risk of cancer of various body organs.
Health Risk for Smokers

nicotine addiction, decreased senses of taste and smell

increased fetal death and disease if mother smokes

lung disease, emphysema, chronic bronchitis, lung cancer

coronary artery disease, angina, heart attacks

atherosclerotic and peripheral vascular disease, aneurysms, hypertension, blood clots, strokes

oral, tooth, gum disease, including oral cancer

Health Risk for Nonsmokers

increase risk of lung cancer over those not exposed to smoke

in infants and children, an increased frequency of respiratory infections (such as bronchitis, pneumonia), asthma, and decreases in lung function

may experience (upon exposure to smoke) acute, sudden, and occasionally severe, reactions including eye, nose, throat, and lower respiratory tract symptoms.