How can I figure out what my baby is allergic to?

It takes some careful detective work and sometimes the help of medical tests to pinpoint the exact cause of an allergy. One clue may be when the allergy attacks occur.

Mold allergies usually develop during damp or rainy weather and can be hard to distinguish from colds. Dust mites or pet allergies often cause morning congestion throughout the year. Pollen-related allergies are more common in spring, summer, and fall.

Unfortunately, sending Fluffy away for a few days won't tell you for sure whether your baby has a pet allergy. Studies at Johns Hopkins University suggest it can take more than a year for cat dander to degrade in a room, for example.

On the other hand, if you take your baby away from the pet (on vacation, for example) and she seems better, then you have a good — but by no means conclusive — lead. (You'd also want to consider that your baby might be allergic to something else in your house.)

If your own sleuthing doesn't give you the answer, it's time to see the doctor. He'll examine your baby and ask lots of questions. If he believes the problem is allergies, he may refer you directly to an allergic specialist or he may suggest a blood test to measure levels of IgE (allergy) antibodies in your baby's blood.

Blood tests may be less accurate than skin tests, especially for infants. So if the blood test does suggest an allergy, the next step for your little sniffler is a skin test. You'll need to see an allergist for that.

During a skin test, an allergist applies small amounts of common allergens to your child's skin. If your baby is allergic to a substance, she'll have a reaction (similar to a mosquito bite) on that spot. Infants may have smaller reactions than older children, but the tests can still be very useful.

"Keep in mind that testing tells you what your child is allergic to at that point, but it may change as your child gets older," says Seattle pediatric allergist Frank S. Virant. If your baby has a negative skin test but continues to have allergy symptoms, have her reevaluated in six to 12 months.

How are allergies treated in babies?

The most important thing you can do is reduce your baby's exposure to the allergen. Here are the best ways to do that for the most common allergens:

Dust mites
Dust mites live in fabrics and carpets and are common in every room of the house. But most children are exposed to the most dust mites in the bedroom, where mattresses and pillows are veritable dust-mite condominiums.

The following steps may seem like a lot of work, but they really help. "Parents who take these steps might expect a 60 to 70 percent rate of improvement in their child's allergies," says Virant, "and this should markedly cut down the level of medication needed for the problem."

• Encase your baby's mattress in an impenetrable cover made of very tightly woven fabric, found at allergy supply stores. Unlike vinyl covers, these provide a useful barrier that's breathable and not crinkly. Avoid big, fluffy comforters and use blankets instead.

• Wash bedding once a week in hot water to kill dust mites. Set your water heater to about 130 degrees Fahrenheit before laundering bedding. Don't forget to turn the water heater back down (to about 120 to 125 degrees) afterward so family members won't scald themselves when they go to wash their hands.

• Avoid piling up stuffed animals in your baby's room — they're dust-mite magnets. Wash the few favorites your baby can't live without in hot water weekly or stick them in the freezer for an overnight killing frost.

• Dust and vacuum weekly or every other week, but make sure your baby isn't in the room when you do it. The action of dusting and vacuuming can stir up residual dust-mite particles in the room. Wet mopping can help prevent this.

• Consider investing in a vacuum cleaner with a HEPA (high efficiency particulate arresting) filter, which traps even microscopic particles that pass right through ordinary vacuum cleaners.

• If your baby has a severe dust mite allergy, consider tearing up carpeting and replacing it with a smooth floor.

• Clean or replace filters on furnace and air-conditioners monthly during seasons they're in use. Have heating ducts cleaned each fall.

Pet dander
If your baby is allergic to a pet, the only foolproof solution is to give the animal away. That's not an easy decision to make, of course, and, understandably, you'll want to consider it only as a last resort.

To keep the dander down, wash your pet frequently. (You can find shampoos that reduce dander in the pet store.) Also keep your pet off the furniture and out of your baby's room.

Molds
Use a dehumidifier and air conditioner when the weather is warm and moist, especially in a wet basement or other areas of your home where mold growth is a problem. If your bathroom is a mold factory, clean it regularly with mold-inhibiting disinfectants, such as a little bleach and water or a natural solution like tea tree oil and water. And consider investing in a better ventilation system.

Mold can often be found growing in closets, attics, cellars, planters, refrigerators, shower stalls, and garbage cans, and under carpets. Even a fake Christmas tree can harbor mold.

Are there any medications that can help my baby?

Yes, but don't give her over-the-counter allergy medicine without talking to your doctor first. He may suggest antihistamines and possibly offer you a prescription. Many of the newer allergy medicines have fewer side effects than other products on the market, though these medications are not approved for children younger than 6 months.

What can I do to prevent my baby from getting allergies in the first place?

At this point, there's lots of conflicting information about preventing or delaying allergies by postponing — or accelerating — a child's exposure to potential allergens.

"Someday we'll be able to look at genetics and really know what a child is destined to be allergic to," says Virant. "But the reality is that, right now, there's nothing that predictably helps."

Of course, if you or your mate is allergic to cats, you won't want a feline in the house anyway. (Ditto for any other allergy-causing animal or substance.) And keeping your home — and in particular your baby's room — clean and as free of mold and dust mites as possible is a good idea, regardless of whether your child has allergies.

Talk to other parents on our bulletin boards about your child's asthma or breathing ailments, food allergies, or skin problems.