CONTRARY TO what's long been advised, people who suffer from the itchy eyes, sniffling and sneezing of allergies need not get rid of their feline companions, said Dr. Thomas Platts-Mills, head of allergy and asthma at the University of Virginia in Charlottesville.

"You usually hear that families [with allergies] should get rid of their cats," he said. "But we do not have enough evidence to say to families with allergies or asthma that they should do this."

In fact, putting the cat out may bring bad luck - or at least worse symptoms, according to Platts-Mills. New studies show that if a child tests positive for allergies to pollen and dust mites, but negative for cat dander, and parents give away the pet, "it's quite possible the child will become allergic to cats," he said.

Another study shows that kids with a dog or a cat in the house get less asthma - with two pets being more protective than one. "One cat will do," Platts-Mills said, "but two - two dogs, two cats, a cat and a dog - is even better."

WHY?

It's all part of the new "dirt is good for you" theory. Current dogma among allergists is that exposing a child early in life to dust, dander and other allergens will help the body to build up immunity against them - just like a vaccination.

Conversely, clean living has an adverse effect: Studies show if that if children escape multiple infections or are not exposed to allergens as infants, their immune systems later overreact to dander or other things that cause allergies.

That's why children who grow up on farms are less likely to develop allergies or asthma than those who reside in hermetically sealed apartments, Platts-Mills explained. Or why in Sweden, 80 percent of kids who are allergic to cats have never had a cat.

THE THANKSGIVING EFFECT

Other new research shows that the protection afforded by having a cat is not permanent, he said. "You raise a kid with a cat who has allergies, but not to the cat; he goes off to college, spends a few months away and comes back to visit," Platts-Mills said. "But now he is allergic to that cat - he has lost that protection."

Dr. John Costa, an allergist at Brigham & Women's Hospital in Boston, said he is also aware of the so-called "Thanksgiving effect."

"Perhaps a lucrative business would be cat hair-filled pillows for college students," he joked.

In truth, though, it is not cat hair that provokes the runny nose, watery eyes and other symptoms of an allergic reaction, but rather their dander, or dead skin flakes, and a protein in the saliva, he said.

The experts spoke Monday at the annual meeting of the American Academy of Allergy, Asthma & Immunology.

Also at the meeting, British researchers reported that contrary to common belief, modern, high-efficiency vacuum cleaners do not rid carpeting of cat dander - in fact, the newer models increase allergen levels just as much as the leaky machines of years past.

Don't let the more expensive models lull you into a false sense of security, said Dr. Robin Gore of the North West Lung Centre in Manchester, England.

Even though they do not leak like old vacuum cleaners, the new high -efficiency particulate air, or HEPA, machines stir things up, raising levels of dander-laden dust in a room, Gore said. The sweeping action may even blow settled dander off the walls and into your nose, he said. Gore compared six vacuum cleaners, four of which were newer HEPA-filter models.

WHAT IF YOU ARE ALLERGIC?

So what should you do if you are allergic to cats? Platts-Mills offered this advice:

• Get rid of carpeting, which harbors allergens.
• Replace upholstery with leather coverings.
• Wash pets at least twice a week.
• Use a HEPA air filter in the rooms. Animal dander is often airborne.
• Cover mattresses and cushions with zippered, plastic casings to cut down on allergen build-up

"No matter how allergic you are to cats, these simple measures can reduce symptoms by 95 percent," Platts-Mills said.