Hay fever, also called seasonal allergic rhinitis, is the allergic reaction set off during a particular season by pollens from trees, grasses and weeds. It is different from year-round allergies that usually are triggered by molds, animal dander and dust mites.

Hay fever is one of the most common chronic diseases in the United States, causing more than 10,000 absences on a typical school day. Children allergic to airborne allergens can have a congested or runny nose, postnasal drip, coughing and itchy eyes. Children who suffer from chronic hay fever often can be recognized by their "allergic shiners" — dark rings under their eyes — and by the fact that they often breathe through their mouths instead of their noses. In more severe cases, hay fever also can interfere with a child's breathing, causing him or her to wheeze.

The best way to avoid or minimize hay-fever reactions is to limit exposure to allergens. Here are some tips:

• Keep windows closed to prevent pollens from entering.
• Keep your child indoors when the pollen count is high, especially on warm, sunny days and in the late morning and early evening
• Minimize activities such as lawn mowing or leaf raking.
• Use air conditioners in those rooms in which your child spends most time to reduce his or her exposure to pollen.
• Wash curtains, rugs and sheets frequently, using detergents that have no dyes, perfumes and other potentially irritating additives.

As much as 10 percent of the population in the United States is believed to be allergic to molds. As much as 80 percent of people with other respiratory allergies are sensitive to molds.

Molds are microscopic organisms that thrive in damp areas, including plants; the bathroom, closets and basement; and air conditioning and dehumidifier filters. Because molds prefer dampness, mold allergies are more prevalent in humid climates.

Here are some tips to help keep your house as clean and dry as possible:

• Eliminate indoor plants to minimize mold growth in damp soil.
• Use dehumidifiers and air conditioners in the house.
• Maintain heating, ventilation and air-conditioning systems. Keep them clean and change the filters frequently.
• Keep your yard raked, and do not leave piles of damp leaves or mulch.
• Leave a low-wattage light bulb turned on in your child's closet to prevent mildew.
• Because fish tanks and bowls can generate moisture, do not put them in your child's bedroom.

House dust is a major cause of year-round allergy symptoms. It is not the dust itself that causes allergies, but dust mites, microscopic spiderlike insects found in the dust. Just a trace of house dust can contain thousands of dust mites. They leave behind excrement and body parts, which can trigger allergic reactions. Dust mites can be anywhere, but they thrive in carpets, textured drapes, upholstered furniture, bookshelves, closets, toys and stuffed animals.

Each female dust mite can produce 20 to 30 offspring, and each mite produces 200 times its weight in fecal matter in its life span. In general, dust mites thrive and reproduce faster in summer weather and humidity. But dust-mite allergies are more common and cause more problems during the winter heating season because the body parts disintegrate into house dust. In addition, children spend more time inside where the windows are closed and the air recirculated.

The most effective way to control dust-mite allergies is to control dust mites through careful attention to house cleaning. That means washing sheets, curtains and other fabrics in your child's room often in hot water with detergents that do not contain irritating ingredients. Consider encasing your child's mattress and pillow in a waterproof or allergy-proof covering.

If cleaning does not relieve your child's allergies, consider removing rugs, drapes and upholstered furniture from your child's bedroom. Research has found that special chemicals for killing mites are no more effective than careful cleaning and are not recommended.

The best way to minimize dust-mite allergy is to limit exposure to dust-mite allergens in the bedroom. Here are some tips:

• Remove feather pillows, down comforters and wool blankets. Substitute bedding made of washable, hypoallergenic synthetic materials.
• Encase bedding in waterproof, or allergy-proof, zippered coverings to entomb the dust mites. This is one of the most effective ways to reduce mite allergies. Remember, children spend about half their time in bed.
• Wash bedding weekly in hot water.
• Leave a spread on the bed during the day to accumulate dust. Before your child climbs into bed, remove the spread and replace it in the morning. Shake out bedding daily when your child is not around.
• Minimize dust. Use washable rugs and curtains and washable stuffed animals, and keep them clean. Washable blinds and an uncluttered decor are more easily kept dust-free. Damp mop the floor and dust furniture frequently with a damp cloth. Damp mopping controls dust on uncarpeted floors better than vacuuming.
• Keep the closet door closed, and hang only those clothes that are in regular use.

Allergies and asthma in inner-city children seem to be on the rise. Between 40 percent and 60 percent of children with asthma and 20 percent and 53 percent of children with allergies have reactions to cockroaches.

Cockroaches most commonly are found in kitchens, bathrooms and basements. The best way to control these allergens is to use a professional exterminator to treat the house or apartment. If you live in an apartment, neighboring apartments must also be treated at the same time. Keep your kitchen clean with no waste food accessible. Avoid leaving food out or bringing food into other parts of the house. This will reduce the likelihood of infestation.

Here are some tips to limit exposure:

• Store all food in sealed containers.
• Wash dirty dishes and silverware immediately.
• Do not leave crumbs on the counter or floors.
• Do not leave out pet food.
• Keep your garbage can well sealed.
• Treat your kitchen with a pesticide or sprinkle boric acid powder in areas where you have seen the bugs. Keep these and all poisons out of the reach of children and pets.
• Do not stack empty grocery bags or newspapers for recycling. Cockroaches live and lay eggs in the piles of paper and cardboard boxes.
• Seal any holes around pipes, windows, doors and baseboards to prevent cockroaches from entering your house.

In children who are allergic to animals, the allergy is actually to pet dander, tiny skin cells that the pet sheds, not to the fur itself. You may be able to limit your child's allergic symptoms by limiting the area in which the pet lives to the kitchen or the yard. However, for many families, having an allergic child means not having a furry pet. For some children the only safe pet is a fish or snake. If you already have a pet and must find a new home for it, include your child in the decision. However, finding a new home for your pet will not alleviate the allergy immediately. Cat dander in particular clings to all kinds of surfaces, which means that it will take time to rid the house of the allergens.

Here are some tips for avoiding or minimizing pet-dander allergies:

• Keep furry pets outside or find them a new home.
• If you keep the pet, keep it out of your child's bedroom at all times.
• Washing your pet can reduce dander for about a week, although this has not been proven to reduce allergic symptoms.
• Wash clothes frequently. Pet dander can cling to clothes, especially to wool.