ALLERGY BASICS: 5 MOST TROUBLESOME ALLERGENS

About 40 million Americans suffer from "hay fever," a disease that allergy specialists prefer to call "allergic rhinitis," because HAY is not to blame and FEVER is rarely a symptom.

If hay is not the culprit, than what is the cause of the stuffy runny nose, watery itchy eyes, sneezing, wheezing and cough? There are plenty of bad actors in the form of allergens out there.

There are dozens of substances that potentially can cause trouble in those of us who are susceptible to allergies. The five most common allergens, according to the American College of Allergy, Asthma and Immunology (ACAAI) are:

1. Trees are usually the first on the scene to cause trouble during allergy season. They are among the earliest plants to start producing pollen, the dust-like, male reproductive parts of plants that cause most allergies. In some southern states, trees can produce pollen as early as January, while pollen production usually begins in April in the north. The oak tree, which is prevalent throughout the United States, produces large quantities of pollen and is a major cause of allergies. Evergreens also can be troublemakers. Cedar, juniper, cypress and sequoia trees all have been known to cause allergies — and if you're allergic to one, you may be allergic to them all. Other suspects include elm trees, which are common in the eastern and Midwestern regions, birch trees, olive trees, sycamores, and poplars, including cottonwoods, balsam and aspen.

2. Grasses usually come along to stir up allergy symptoms after the trees are through pollinating — typically from late spring to early summer. Common culprits are timothy grass, Bermuda grass, sweet vernal, red top and some blue grasses.

3. Weeds are guilty of causing most of the allergy misery that occurs in the late summer and early fall. No. 1 on the Most Wanted List is ragweed — which affects as many as 75 percent of all hay fever sufferers. Ragweed is found in virtually every region of the United States and, with 17 different species of the weed, there's plenty of pollen to keep people sneezing and sniffling until frost. Other common weed allergens are sagebrush, found predominantly in the west, pigweed and goosefoot pollen.

4. Molds are microscopic plants that reproduce by sending tiny spores into the air. They thrive in areas that are warm, dark and moist. Unlike pollen, which appears only in the warm weather months, mold can lurk in your house year-round.

5. Dust mites are small (hundreds can live in a single gram of dust), eight-legged creatures that belong to the same family as spiders, chiggers and ticks. These culprits are hardy creatures that live well and multiply easily in warm, humid places. Favorite hideouts include carpets, upholstered furniture, bedding, clothes, soft toys and the fur of pets. The intruder is particularly malicious when trapped inside a closed-up house when the weather turns cool.