More than 8 million people in America, many of them women, suffer from excessive sweating (also known as hyperhidrosis). To find out why some women perspire more than others, and what you can do about it, we turned to skin expert Doris Day, M.D., a cosmetic dermatologist in New York City.

The Basics on Excessive Sweating

Your body contains 2 to 4 million sweat glands, with most concentrated on the soles of the feet, palms, and armpits. These glands, activated by nerve endings in the dermis (the deepest layer of skin), respond to chemical messages from the brain. Changes in temperature, hormone levels, and activity cause a secretion of water and electrolytes (sweat). This controls the body's internal temperature by cooling the skin.

What Triggers It

You're most likely to sweat when you're hot, but here are some other reasons:

Stress: Anxiety causes the glands to release sweat. Stay calm and dry with these 10 ways to de-stress anytime, anywhere.

Medical conditions: Hormonal changes, diabetes, and thyroid disorders can all cause excessive perspiration. But excessive sweat isn't the only result of hormonal changes. Find out when hormones are the real reason why you feel bad.

Genetics: If your parents suffer from hyperhidrosis, you're at an increased risk for excessive sweating. But before you ask your doctor for prescription-strength deodorant, it's important to be sure you really do have hyperhidrosis. Look for these signs to find out if your sweat level is normal.

Simple Sweat Solutions

Wear breathable fabrics: Wearing thin layers of 100 percent cotton helps reduce sweating. Try this organic cotton workout gear.

Take a long, deep breath: Breathing slowly through your nose relaxes the nervous system and reduces excess sweating. If that doesn't work, these three stress busters can help you stay cool and dry.

Use an antiperspirant deodorant: This will block pores, preventing sweat from mixing with bacteria on the skin, which creates odor. Opt for one labeled "clinical strength," like Secret Clinical Strength ($10; at drugstores), if you have excessive sweat-it contains the highest amount of aluminum chloride available sans Rx.

Ask your doctor for a prescription version: One like Drysol has 20 percent more aluminum chloride than over-the-counter options.

SHAPE'S top pick:Origins Organics Totally Pure Deodorant ($15; fights odor naturally with a blend of essential oils. Get more of SHAPE's award winning deodorants, sunscreens, lotions and more.

Expert Sweat Solution

If the above options aren't cutting it, ask your doc about Botox injections (unsure about Botox? Learn more), which temporarily immobilize the nerves that stimulate the sweat glands, says dermatologist Doris Day. Each treatment lasts six to 12 months and costs $650 and up. The good news? Hyperhidrosis is a medical condition, so your insurance may cover it.

The Bottom Line on Sweat

Sweating is natural, but if it happens at odd times, see your M.D. to find out what's to blame.

More ways to deal with excessive sweat: