If you’re a smoker and you’re thinking of quitting or have tried to quit before, chances are you already know all the reasons you should. There are the external factors like bad breath, yellow teeth, stained fingers and lips, age spots, and wrinkles. Then there are the things you can’t see, like an increased risk for lung cancer, emphysema, fertility problems, heart disease, and stroke.

Who Smokes?

Smoking crosses all racial, gender, and socioeconomic lines. According to the Centers for Disease Control and Prevention (CDC), more than 45 million American adults smoke—that’s almost 20 percent of the adult population (CDC, 2012).

More men light up than women—21 percent versus 17 percent of women. And it isn’t just adults. CDC studies show that 20 percent of U.S. high school students smoke cigarettes too (CDC, 2012).

What's in a Cigarette?

Cigarettes are made with dried tobacco leaves that naturally contain the drug nicotine. Cigarette manufacturers add chemicals like ammonia, tar, lead, cyanide and other ingredients, like cocoa, coffee, and menthol, to change the flavor of the tobacco in an attempt to make smoking more enjoyable.

According to the American Cancer Society (ACS), more than 7,000 different chemicals have been identified in cigarettes and cigarette smoke. Of those 7,000 chemicals, 60 are carcinogens, meaning they’re known to cause cancer (American Cancer Society, 2013).

Recently, federal legislation required cigarette manufacturers to provide the Food and Drug Administration (FDA) with a list of harmful or dangerous chemicals in their cigarettes. However, unlike medications, spirits, and most foods tobacco products are unregulated for the most part. This means that some potential health risks—beyond what we already know from years of consumer use—are still being discovered.

Smoking, Pregnancy, and Fertility

Smoking and tobacco use affect reproduction and fertility. Research shows that men who smoke have lower sperm counts, and the sperm they do have is often misshapen and has a harder time moving, making conceiving more difficult. Experts also believe smoking affects sperm DNA, which may lead to developmental and physical health problems in a child.

Women who are pregnant and still smoking are damaging the current and future health of their unborn child. Babies born to mothers who smoke are about 22 percent more likely to be born prematurely, according to the March of Dimes, and those who do make it full term are more likely to have a low birth weight (March of Dimes, 2012). Babies born to mothers who smoked during pregnancy are also at a greater risk of sudden infant death syndrome (SIDS).

Smoking and Disease Risk

The leading cause of death in American men and women is heart disease. Smoking increases your risk for heart disease two to four times compared to a nonsmoker. The same thing goes for your risk of stroke. Smoking narrows your blood vessels and arteries, which may lead to peripheral artery disease (PAD), the obstruction of the large arteries in your arms and legs. If you continue to smoke, PAD can cause a range of complications including pain, muscle deterioration, and eventually muscle death.

Smoke damages your lungs and your airways, putting you at greater risk for respiratory disease. In men, the risk of developing lung cancer increases 23 times if you are a smoker. Lung cancer is the leading cause of cancer death in women, and smoking increases a woman's chance of the disease by 13 times that of nonsmokers (American Lung Association, 2013). Many smokers will also develop a chronic obstructive pulmonary disease (COPD) , which is one of a few diseases, like bronchitis or emphysema, that restrict airflow into and out of your lungs, making breathing increasingly difficult.

Smoking and Death

Smoking remains the number one cause of preventable disease and death in American adults, according to the American Heart Association (AHA). In addition, each year secondhand smoke kills tens of thousands of people who never took a single puff in their lives. The AHA explains that on average, smokers die 13 to 14 years earlier than nonsmokers (AHA, 2011). If you don't quit, you could be one of the estimated 443,000 adults who die each year from a disease or complication attributable to smoking (CDC, 2012).

Here's some good news, though: The moment you are no longer a smoker, your risks for many diseases and health complications begin to decrease. In fact, according to the American Cancer Society, one year after you smoke your last cigarette, your risk for heart disease is reduced by half.

Fifteen years later, the risk for heart disease is similar to that of someone who has never lit up. The same is true for the risk of stroke (American Cancer Society, 2013). Your health and the fate of your health are not set in stone. You can change your future by making the decision to quit today.