Let's face it: There's no body part women obsess about more than breasts -- their size, shape, sag factor, and whether those strange pains stem from monthly PMS hormones or something more ominous, like breast cancer.

Wearing a good exercise bra when you're young can stave off droopiness later.

All this nipple-gazing makes sense: Your chest changes over the decades, meaning you're continually facing new questions and concerns. To help you troubleshoot at every stage, Health asked experts to get age-specific. Here's the latest on how to keep your breasts healthy and looking great -- now and in the years to come.

Your breasts in your 30s

Typically, in your 30s your breasts still have good elasticity and tone, says Shirley Archer, a health-and-fitness educator at the Stanford University School of Medicine and author of "Busting Out. " If you have kids now, you'll notice changes post-baby. While your breasts get bigger during the actual pregnancy, you may, alas, permanently go down a half-cup or cup from your original size once you've given birth and/or breast-fed. (This phenomenon is called breast involution, a process where the milk-making system inside the breast shrinks because it's not needed anymore.)

Your most common concern:

Breast pain. Many thirtysomethings have fibrocystic breasts, a grab bag term for tender lumpiness resulting from hormonal changes, says Holly Smedira, M.D., a medical breast specialist at the Cleveland Clinic Breast Center. Although uncomfortable, the condition is benign and doesn't increase breast-cancer risk. Cutting back on caffeine may help alleviate some of the pain, as may taking evening primrose oil (1.3 grams orally twice a day), a natural form of fatty acid believed to interfere with the body's production of prostaglandins (inflammatory compounds that trigger breast pain). For severe cases, doctors sometimes prescribe Danazol, a steroid derivative that decreases levels of the reproductive hormones FSH and LH, or tamoxifen, a breast-cancer drug that helps relieve breast pain by blocking estrogen receptors, thus preventing estrogen's effect on breast tissue. Health.com: 4 healthy breast tips for every year

Best breast-cancer-screening strategy:

Talk to your doctor. Discuss having a baseline mammogram between the ages of 35 and 40, suggests Julia Smith, M.D., director of the New York University Cancer Institute Breast Cancer Screening and Prevention Program. You should also get a yearly breast exam from your gynecologist and do monthly breast self-exams. Although the American Cancer Society issued new guidelines for breast cancer screening in 2003, making self-exams optional, experts say they're still a must-do. "The more you examine your breasts, the more likely you are to differentiate between normal hormone-related bumpiness and a potentially precancerous growth," Smith says.

A woman who is at higher risk (that is, one who has a family history with one or more first-degree relatives with breast or ovarian cancer) should begin having regular annual mammograms at least 10 years earlier than the age at which her relative got her cancer diagnosis. So, if your mom found out she had cancer at age 45, you should start having mammograms done at age 35. Also, if you have a strong family history of the disease (two or more first-degree family members like a mother or grandmother), ask your doctor about receiving genetic screening to see if you're a carrier of the BRCA gene and ask about an annual MRI.

Best breast-saving move:

Wear a good exercise bra. This will help stave off future droopiness, Archer says. When you run sans bra, your breasts bounce up and down 2.6 inches for every step you take, according to a recent study done at the University of Portsmouth in England. The reassuring news: The study also found that wearing a sports bra reduces bounce by 74 percent. Health.com: How to buy a more supportive bra

"I recommend women do the bounce test when trying on exercise bras. If your breasts move when you jump up and down, you're not getting enough support," Archer says. If one sports bra doesn't do the job for you, she adds, try wearing two.

Good news!

Your breast-cancer risk is still very low -- only 5 percent of all cases occur in women younger than 40, according to the ACS. (Your risk during this decade is about 1 in 233, according to the National Cancer Institute.) One way to lower your odds even further: breast-feed. It protects older moms against the increased risk of breast cancer noted for women who have their first child after age 25, according to a recent University of Southern California study.

Your breasts in your 40s

In your 30s, your chest is made up mostly of breast tissue. But as you enter this decade, the percentage of fat in your breasts increases, breast specialist Smedira says. Fat's less likely to withstand the effects of gravity, so your breasts will start to droop and sag. Health.com: Dermatologists' advice for your decolletage

Your most common concern:

Breast cysts. As breasts change from their lactational state, fluid can be trapped in the ducts, causing fluid-filled cysts, Smedira explains. They are harmless (though sometimes painful) and can be evaluated by ultrasound and then aspirated if they are large or uncomfortable. They won't increase your future risk of cancer, Smedira says.

Best breast-cancer-screening strategy:

Annual mammograms. Starting at age 40, "it's crucial to get a mammogram every year, especially since the test has only about 80 percent sensitivity in younger, premenopausal women," Smith stresses. "This way, if an early stage cancer is missed one year, it most likely will be caught the next."

It's also important to do monthly at-home breast checks and see your doctor for yearly breast exams, says Rachel Brem, M.D., vice chairman of radiology and director of breast imaging at the George Washington University Medical Center in Washington, D.C. A must for premenopausal women: Find a center that offers digital mammography, which takes an electronic image of your breasts and stores it directly into a computer, Brem says. A recent National Cancer Institute study found that digital mammography picks up more cases of cancer, but only in women who are premenopausal and/or have dense breasts. Health.com: The right mammogram for you

Best breast-saving move:

Stand up straight. "As a woman gets older, her back muscles weaken, and she tends to slouch, which gives her breasts the appearance of hanging down to her belly button," Archer says. "If you strengthen your upper-back and torso muscles, you'll have a nice open chest and shoulder line, which will help make your breasts look perkier."

Try the back--shoulder blade squeeze:

Stand with shoulders relaxed and arms at your sides. Hold the end of an exercise band in each hand in front of your body. Exhale as you squeeze shoulder blades together, keeping your shoulders relaxed, torso stable, and wrists flat; inhale as you return arms to starting position. Do 8--12 reps, working up to 1 minute. And increase band resistance as you get stronger.

Good news!

Premenopausal women who get three servings of low-fat dairy every day and pop a calcium supplement with vitamin D daily reduce their risk of breast cancer by about 40 percent, according to a Harvard study.

Your breasts in your 50s:

You may notice some slight shrinkage. As you get older, hormonal changes cause body fat to accumulate in your lower regions -- fat often decreases in the face or breasts and increases in the butt or thighs, Archer explains. You'll also notice more sagging because, as menopause approaches, fat (which is more gravity-prone) replaces almost all breast tissue, and skin loses elasticity. Age also stretches out the Cooper's ligaments. These fibrous, semielastic bands of tissue are found in breasts, and "they're like rubber bands that get stretched over time," Archer says. Health.com: How your age affects your cancer risks

Your most common concern:

Breast cancer. Your risk of developing the disease is now 1 in 38, the NCI says. So in your 50s, it's more important than ever to get to a healthy weight. Several major studies have found a link between postmenopausal weight gain (especially if you tend to gain around the waist) and breast cancer. "I recommend that every woman in this age group measure her waist, which should be less than half her height in inches," Smedira says.

Best breast-cancer-screening strategy:

Annual mammograms. These are a must, as are physical examinations by your doctor and monthly self-exams.

Best breast-saving move:

Chest exercises. While nothing will magically save you from sagging, doing chest moves two or three times a week will pump up breasts temporarily (by increasing blood flow to the area) and tone underlying muscles. Here's a good exercise to try before a big event: Lie on your back across a bench with your knees bent and your feet on the floor. With both hands, hold a dumbbell directly over your chest. Inhale as you lower the weight in an arc past your head, going as far as shoulder flexibility allows. Pause, then exhale as you lift the weight overhead in an arc until your hands are above your torso. Start with 8--12 reps; work up to 1 minute.

Good news!

Since your breasts are fattier now, mammograms can better detect cancer: The false-negative rate drops from about 25 percent under the age of 50 to about 15 percent, Brem says. E-mail to a friend

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