A little sweat can be a very good thing: You wouldn't want to plant a summer garden, ride your bike or a run a marathon without it.

Sweat helps keep you cool and healthy. But too much sweat at the wrong time? Not cool. "There are people who put on a clean shirt and sit down in an air-conditioned room and within half an hour have a dinner-plate-size wet spot on each side of their shirt," says David Pariser, a Norfolk, Va., dermatologist.

Pariser, who is president of the American Academy of Dermatology, says sweaty hands can be especially vexing: He has met lawyers who ruin documents with their wet hands, and one police officer whose hands were so sweaty he could not fire a gun. A simple handshake can be mortifying for such folks, he says.

"I think I was even dumped once because of it," says Therese Hernando, 26, a Lake Forest, Calif., office worker. "A boyfriend said my hands were too sweaty."

The medical name for extreme sweating is "hyperhidrosis." It can affect the underarms, hands, feet and face. Nearly 3 percent of Americans say they sweat too much, according to a study published in 2004 in the Journal of the American Academy of Dermatology. One-third of those with heavy underarm sweating said it was "barely tolerable" or "intolerable" and interfered with daily life.

Such sweating can be socially crippling, says study co-author Dee Anna Glaser, a St. Louis dermatologist and president of the International Hyperhidrosis Society, a non-profit group that gets money from companies that sell treatments for the disorder. "It does not kill people, but it can really impact their ability to get along in the world."

And it can have medical consequences: People with hyperhidrosis are at increased risk for skin infections, ranging from warts to athlete's foot to invasive bacteria, says Hobart Walling, a Coralville, Iowa, dermatologist. He reported his findings in May in the dermatology journal.

Doctors say they can help. Treatments include:

Antiperspirants. Prescription and over-the-counter "clinical strength" brands help at least one-third of people with heavy underarm sweating, Walling says. Key tip: Apply it at bedtime, even if you plan to shower in the morning.

Iontophoresis. In this unlikely-sounding treatment, patients put their hands or feet in shallow trays of water with a device that emits a mild electrical current. It's thought that the electricity and minerals in the water work together to slightly thicken the skin, blocking the flow of sweat. The downside: Each home treatment takes 20 to 40 minutes and must be repeated several times a week, Pariser says.