Smoking during pregnancy increases the risk for pregnancy complications, premature delivery, a low birth weight infant, and stillbirth.

Babies whose mothers smoke while pregnant and babies who are exposed to secondhand smoke after birth are more likely to die from sudden infant death syndrome (SIDS) than babies who are not exposed to cigarette smoke. These babies also have weaker lungs than other babies, which increases their risk for many health problems.

Smokeless tobacco products are not a safe replacement for smoking. These products have significant health risks. All tobacco products contain the highly addictive drug called nicotine. Smokeless tobacco products generally deliver more nicotine than cigarettes. The use of these products can lead to nicotine addiction and dependence. Youth who use smokeless tobacco also are more likely to become cigarette smokers.

Smokeless tobacco contains more than 25 cancer-causing compounds, including arsenic and formaldehyde. People who use these products have an increased risk of developing cancers of the mouth and throat.

Smokeless tobacco use also is strongly associated with the formation of skin lesions in the mouth. These include leukoplakia (lu-ko-pla-kee-uh), which are white patches that can turn into cancer over time, and erythroplakia (e-rith-ro-pla-kee-uh), which are red patches that have a high potential for becoming cancerous.

Smokeless tobacco also is strongly associated with gum recession. Gum recession not only is unsightly; it increases one’s risk of getting cavities on the tooth roots and can make teeth sensitive.

A hookah pipe is used to smoke a tobacco mixture called shisha. Shisha contains tobacco and flavorings such as fruit pulp, molasses, and honey. The hookah pipe uses coals to heat the shisha, and the smoke that is created passes through tubes and water so it is cooled before it is inhaled.

When smoking shisha, a person not only inhales tobacco smoke but also inhales smoke from the burning flavorings. Because hookah smoking is a relatively new activity in the United States, no research is available on the health effects of inhaling smoke from the substance.

According to the American Cancer Society, several types of cancer, as well as other negative health effects, have been linked to smoking a hookah pipe. Passing the smoke through water may remove some compounds, but research shows that many toxins remain in the water-filtered smoke. These toxins include nicotine, which is the highly addictive compound in tobacco smoke. Consequently, hookah users suffer the same effects of nicotine use (e.g., increases in blood pressure and heart rate, changes in dopamine production in the brain, etc.) that occur in cigarette smokers.

Some people believe that smoking only in social situations or smoking only a few cigarettes a day is not harmful. Although health risks related to smoking increase with the amount smoked and the length of time a person smokes, there is no safe amount to smoke.

Any time that tobacco smoke touches a living cell, some damage is done. When a person inhales cigarette smoke, the smoke enters the lungs and damages lung tissue. Nicotine in the smoke is then rapidly absorbed into the blood. Within 10 seconds, nicotine starts affecting the brain. Nicotine quickly increases heart rate and blood pressure and restricts blood flow to the heart. Nicotine also lowers skin temperature and reduces blood flow in the legs and feet.

A major concern is that most people who start as casual smokers think they can stop whenever they choose. However, studies show that many of them become regular smokers.

Nicotine reaches the brain within 10 seconds after smoke enters the lungs and affects the body. Nicotine raises the heart and respiration (breathing) rates. Nicotine also causes more glucose (blood sugar) to be released into the blood, which may explain why smokers say they feel more alert after smoking.

Nicotine also causes the brain cells to release an unusually large amount of a chemical called dopamine. Dopamine stimulates pleasure centers in the brain, making the smoker feel good.

The effects of nicotine do not last very long. When the effects wear off, the smoker feels a strong urge to smoke again to get more nicotine.

Repeated doses of nicotine alter the brain’s activities. The brain reduces the amount of dopamine that it produces. The number of receptors that carry dopamine to the cells is also reduced. When this happens, the smoker needs nicotine just to have normal levels of dopamine in the brain. If the level of dopamine drops, the smoker feels irritable and depressed.

Both young and older smokers can become addicted to nicotine. In adults, nicotine addiction is linked to the amount and frequency of tobacco used. In teens, nicotine addiction appears to be linked to the length of time they have been regular tobacco users. Teens who only smoke small amounts but who smoke daily are still at high risk of becoming addicted to nicotine.

Nicotine is the highly addictive drug found naturally in tobacco. Nicotine is found in cigarettes, cigars, smokeless tobacco, shisha (the flavored tobacco smoked in a hookah or water pipe), bidis, and kreteks (clove cigarettes). Even if a tobacco product is marketed as “all natural,” it is still addictive because of its nicotine content.

Nicotine meets the following criteria for an addictive substance:

(1) The user’s behavior is largely controlled by a substance that causes mood change, primarily because of the substance’s effects on the brain.
(2) The individual will continue to use the substance, often putting it before other priorities.
(3) The person develops a tolerance for the drug, so increasing amounts are needed to create the same effect.
(4) Withdrawal symptoms occur if the person does not use the drug.
(5) A strong tendency for relapse exists after quitting.

The amount of nicotine, cotinine, carbon monoxide, or other components found in the body varies with the amount of tobacco used, the type of product used, and a person’s smoking behavior (e.g., how deeply the person inhales). However, within 3 to 4 days of quitting, any by-products found in the body should be at levels low enough to indicate that the person is no longer actively smoking.

Measuring concentrations of nicotine or its breakdown products (e.g., cotinine) in body fluids such as blood, urine, or saliva can reveal whether a person currently smokes and about how much the person smokes. Other tests for tobacco use measure concentrations of carbon monoxide or other gases in a person’s breath.

People exposed to secondhand smoke may have a measurable level of nicotine or nicotine by-products in their bodies, but the level is the result of passive inhalation rather than active tobacco use. If you are scheduled for testing, you may want to avoid closed areas where people are smoking for a day or two before the test is given.

Although only a small number of studies have looked at the relation between smoking and erectile dysfunction, research findings suggest that smoking may be associated with an increased risk for this condition. More studies are needed, however, before researchers can conclude that smoking is causally related to erectile dysfunction.

Research also suggests that cigarette smoking may affect the amount of semen and sperm produced and adversely affect sperm quality.

Women who smoke have more difficulty becoming pregnant and have a higher risk of never becoming pregnant. Those who smoke during pregnancy also have a greater chance of complications, including placenta previa, a condition in which the placenta grows too close to the opening of the uterus, and placental abruption, a condition in which the placenta prematurely separates from the wall of the uterus.

In addition to complications, women who smoke during pregnancy are at higher risk for premature birth, a low birth weight infant, stillbirth, and infant mortality.

Certain agents in tobacco smoke can damage important genes that control the growth of cells, which increases a person’s risk for many types of cancer.

Lung cancer is the leading cause of cancer death. About 87 percent of lung cancer cases are caused by smoking. Smokers are about 20 times more likely to develop lung cancer than nonsmokers. Smoking also causes cancers of the mouth, throat, larynx (voice box), and esophagus, and it increases a person’s risk of developing cancer of the pancreas, kidney, bladder, cervix, and stomach. Smoking may also contribute to the development of acute myeloid leukemia, which is a cancer of the blood.

For smoking-attributable cancers, the risk generally increases with the number of cigarettes smoked and the number of years of smoking. Risks generally decrease after a person quits completely. Ten years after quitting, the risk of developing lung cancer decreases by as much as half.