If I were to tell you that smoking causes cancer, ups your risk of heart attack and COPD, and could subtract as many as ten years from your expected life span, I'm guessing you'd nod and smile -- after all, you've heard it all before. But what about damage that's a little more, well, personal? What if I told you that smoking could wreck your chances of having a baby, make you look 60 when you're 45, and -- for the guys out there -- sabotage your abilities in the bedroom? And more? Here are 5 surprising reasons to quit smoking -- and how you can reverse past damage once you do.

Reason #1: Smoking sabotages sexual prowess.

To put it bluntly, men who smoke have a harder time getting and staying up, studies show. In fact, a study published in Addiction Behavior demonstrated that smoking just two cigarettes could cause softer erections in male smokers. And numerous studies have shown that men who smoke have as much as a 60 percent higher rate of erectile dysfunction than nonsmokers. Men who smoke are also more likely to be shooting blanks, and over time cigarettes may even cause the male equipment to shrink.

How smoking harms virility: Nicotine functions as a vasoconstrictor, which means that it constricts blood vessels, impairing blood flow. (This effect is responsible for the "rush" that sometimes comes with smoking.) Since erections depend on blood flow, it makes sense that smoking would affect a man's ability to get and maintain an erection. The damage is cumulative, and nicotine has been shown to cause, over time, permanent damage to arteries. Animal experiments have also found that nicotine decreases testicle size and blocks sperm production.

How quitting helps: The studies are mixed on this topic because it depends how long you've smoked, how much you smoke, and whether permanent damage has occurred to the arteries. But doctors report that many men who quit smoking notice an immediate improvement in the strength and length of their erections. The good news is that over time, at least some damage to the vascular system can heal. And the sooner you quit, the less long-term damage you do to arteries and blood flow to vital parts.

Reason #2: Smoking makes you lose your teeth.

Forget stains; yes, smokers have brown teeth, but that's not the surprise. The "you're kidding" factor comes when you talk to dentists and discover that smokers are twice as likely to lose teeth as nonsmokers. The reason? Gum disease. Heavy smokers, according to one study, are six times as likely to get periodontal disease as nonsmokers. And getting good dental care doesn't mitigate the damage; one study found that even after five years of periodontal treatment, smokers lost teeth at twice the rate of nonsmokers.

How smoking damages gums and teeth: The periodontal tissue, which includes both gum and bone, holds the teeth in place and provides the oxygen and nutrition necessary to sustain the living tooth. By reducing blood flow, smoking starves the periodontal tissue of oxygen and nutrients, causing it to age prematurely. Smoking also inhibits the body's ability to fight off infection from the bacteria that naturally occur in the mouth, leading to chronic inflammation. Eventually the bone begins to erode and the teeth loosen and fall out.

How quitting helps: Experts say that within months of quitting smoking, circulation is restored to normal or near-normal levels. And studies show that within a year, the risk of developing heart disease drops to half that of people who still smoke, suggesting that cardiovascular damage isn't permanent. Your body will regain its ability to fight off infection, including the gum disease that can cause you to lose your teeth.

Reason #3: Smoking makes breasts sag.

Really?! Yes, really. In the past year, researchers have actually named smoking as one of the top causes of sagging breasts. British plastic surgeon Brian Rinker studied 132 American women in their mid-30s who sought breast lifts and discovered that breastfeeding wasn't associated with saggy breasts -- but smoking was. (Guys, you'd be forgiven if you brought this information to your partner's attention.)

How smoking causes breasts to sag: Scientists don't know exactly how smoking contributes to breast ptosis, which is the medical term for drooping breast tissue. But Rinker attributed the results to the fact that smoking breaks down elastin, the protein fibers in skin that lend it firmness and elasticity. Smoking also damages breast skin the same way it does the face, depriving it of oxygen and nutrients.

How quitting helps: Once breasts are lower and flabbier, nothing's going to make them lift back up short of surgery. But the loose crepey skin that makes them look saggier will improve rapidly once you quit smoking. Try this test: Pinch the skin on the inside of your arm and on the side of your breast under your arm. Look and see how much loose skin you can pull together. Six months after quitting, try the same test and you should see a dramatic improvement in tone and elasticity. Meanwhile, the sooner you quit, the sooner you halt the process that's causing them to droop.