1. Breasts get fat. In your 20s, your boobs are made up of fat, milk glands and collagen -- the connective tissue that keeps them firm. "But as you age, the glands and collagen shrink and are replaced by more and more fat," explains Laurie A. Casas, a plastic surgeon and associate professor of surgery at Northwestern Feinberg School of Medicine. Instead of making your bra size go up, however, the added flab can send breasts down, closer to the floor, if you catch our drift. Wearing an underwire bra (whether you're an A-cup or a D) can help fight sagging over time.
2. But they weigh less than you think. That surge in the scale isn't your set's fault: An A-cup clocks in at only a quarter pound; a B, about half a pound; a C, three-quarters of a pound; and a D, around one pound.
3. They're thin-skinned. "Because they were stretched as you developed, breasts have thinner skin than the rest of your body, leaving them susceptible to dryness," says Laurie Polis, a dermatologist in New York City. Keep your pair supple by moisturizing them with a firming cream that stimulates collagen and elastin growth and has UV protection and retinol to prevent wrinkling. Don't ignore your nipples either; they're also prone to dryness. Give them a daily dose of a superemollient moisturizer, like Vaseline or Aquaphor.
4. Stray strands are normal. Almost all women have some degree of nipple hair. "Having 2 to 15 dark, straight strands growing at one time is extremely common," explains Debra Jaliman, M.D., a clinical instructor of dermatology at Mount Sinai School of Medicine in New York City. The general rule is, the darker your skin and the hair on your head, the more nipple hair you'll have. If the hair bothers you, waxing it away is fine. But if you have only a few strands, it's easier to tweeze: Clean the area with alcohol, pluck each hair, then wipe down the affected skin with an antibacterial lotion to prevent infection. That should give you a week or two before you have to break out the tweezers again.
5. Each pair has its own point. Not only do nipples come in varying sizes, they also point in different directions. "Whether your nipples go up, down, left or right depends on their structure and where the areolae sit on the breasts," says Dr. Casas. "Some areolae rest a little higher, which can angle the nipples upward. Others rest lower or are closer to the edges of the breasts." Some women even sport a pair that aim in opposing directions.
6. They have their own monthly cycle. "Fluctuating hormones cause your breast tissue to change week by week," explains Hilda Hutcherson, M.D., associate professor of obstetrics and gynecology at Columbia University. In the days after your period, breast tissue feels smoothest, thanks to even hormone levels. Midcycle, your nipples may become more sexually sensitive, due to increased estrogen levels. Finally, the week before and during your period, extra progesterone may leave your set swollen, bumpy and tender. Popping an OTC painkiller and cutting back on caffeine can help quell the ache.
7. There's a right time to take them to the doctor. Because your boobs are at their smoothest and least tender the week after your period, it's the best time to have your gyno check out any unusual lumpiness or swelling. "Your doc will have an easier time diagnosing the problem because it'll be easier to detect something abnormal," says Dr. Hutcherson.
8. Four million of them are fake. About two million women in the United States have breast implants, with 250,000 going under the knife each year. But if you think it's mostly Jenna Jameson wannabes getting boob jobs, read on: The average age of a woman who gets implants is 34, and 90 percent do it after they have had kids. "Most women increase two cup sizes," says Leroy Young, M.D., chair of the breast surgery committee of the American Society for Aesthetic Plastic Surgery. No, they're not always happy with the results: Six percent of women who sport a fake set return for a size adjustment or to have them taken out altogether.
9. But implants still pose health risks. Though research hasn't conclusively linked implants to serious health ills like immune-system disorders or an increased risk of cancer, both silicone (which has been unavailable to most women in the U.S. since 1992) and the far more common saline type can still cause side effects. "In less than 10 percent of cases, either kind can deflate, leak or become wrinkled, requiring another operation to replace the damaged implant," says Dr. Casas. Another complication is called capsular contracture, which is when the scar tissue that naturally forms around implants tightens, causing the breast to feel hard. "This also requires another procedure to fix," she adds. And as with any operation, there's the small but dangerous risk of infection and excessive bleeding.