For millions of people, pretty earrings are a synonym for "ouch."

When they wear clip or pierced earrings, their ears begin to itch and burn. Within a couple of hours, the pain, weeping skin and, in extreme cases, bleeding and pus force them to remove the earrings.Their condition is called contact dermatitis, caused by contact with material to which the victim is allergic or to which she has become sensitized - in this case the metal in the earrings.

For years after Connie Bradley of Pittsburgh pierced her ears, she experienced no difficulties. Her allergy developed gradually.

"I'd have constant itching around my ears; sometimes the earlobe would swell. I decided I definitely wouldn't wear any more three-for-a-dollar earrings."

After her ears healed, she had her ears pierced again, and wore expensive diamond and gold earrings. "It lasted about a year . . . before my ears started itching again. I felt bad - I'd bought all these earrings."

Her story is familiar to many women. Studies of nickel-plated earrings show that 10 percent to 15 percent of wearers suffer contact dermatitis, according to Dr. Barry Asman, an allergist.

Michael Bow, marketing director for an ear-care company called E'arrs, puts the number of sufferers much higher, citing a study in which 25 percent of women had contact dermatitis.

Physicians say sufferers are most likely to be allergic to nickel, a common jewelry filler.

"Most women allergic to common metals, such as nickel or copper, can wear solid gold, as long as it's pure," says Dr. Carol Zinn Congedo, an ear, nose and throat specialist. Allergies to pure stainless steel are also rare.

Asman says it's important to avoid nickel from the start - needles used to pierce the ear and studs or posts used afterward shouldn't contain a drop of nickel.

"Once you acquire a nickel sensitivity, you have it forever," he says.

Unfortunately, nickel is hard to avoid, and the label "stainless steel" doesn't rule out the possibility.

Neither does the label 14- or 18-karat gold. Fourteen-karat means 14 parts gold to 10 parts alloy; 18-karat, 18 gold to 6 alloy, says jeweler James Mongelli. And those alloys could contain nickel.

A chemical test can determine if jewelry contains nickel. Allertest-Nt, manufactured by Allerderm Lab in Mill Valley, Calif., is a kit ($10.50 plus $2.50 shipping fee) that determines if nickel is present. To order call (800) 365-6868.

In the study Asman cited, 95 percent of those who became sensitized had pierced ears. Physicians speculate ear holes provide a path to penetrate skin tissue.

According to Asman, earring wearers experience more trouble during summer, perhaps because perspiration dissolves nickel and makes it easier for the body to absorb. This theory suggests it would be wise to remove jewelry before engaging in sweaty activities.

Once someone has contact dermatitis, doctors emphasize the best thing to do is to stop wearing the offending earring forever.

If inflammation is present, Congedo advises keeping the lobes clean, using topical steroid.

- HOW TO PROTECT SENSITIVE EARS FROM METAL ALLERGIES

One way to avoid contact dermatitis is to prevent earring metal from touching the ear. A homemade protector could be nail polish or transparent tape.

Following are some products designed to prevent contact dermatitis:

- E'arrs, based in Gainesville, Ga., offers patented Pierced Ear Protectors. The protectors, made of soft polyethylene sleeves, slip over posts and loops to shield the ear from metal contact.

- Roman Research Inc., based in Pembroke, Mass., offers "about a thousand styles of 100 percent hypo-allergenic earrings," says marketing director Eddie Andresen.