The 5 Most Common Allergies



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Some 50 million Americans suffer from allergies. These disorders start with a fateful mistake: Your immune system misjudges a harmless substance you've ingested and interprets it as a dangerous pathogen. From then on, your system raises its defenses every time it detects particles of the offending substance, or allergen, triggering a bevy of unpleasant side effects, such as wheezing, sneezing, itching and swelling. If you find yourself doing those things a lot, you might be allergic to one of these five things - the most common allergens, according to the American College of Allergy, Asthma and Immunology (ACAAI).



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Weeds are guilty of causing most of the allergy misery that occurs in the late summer and early fall. Top on the list of offenders is ragweed. Found in virtually every region of the United States, the 17 different species of this weed keep people sneezing and sniffling until frost. Other common weed allergens are sagebrush, found predominantly in the west, pigweed and goosefoot pollen.


Mold growing on a clementine.

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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.

Dust mites

North American house dust mite, a major creator of allergens.

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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.


Bermuda grass

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Grasses usually come along to stir up allergy symptoms after 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.


Scanning electron microscope image of pollen grains from a variety of common plants: sunflower, morning glory, prairie hollyhock, oriental lily, evening primrose and castor bean.

(Image credit: Public domain image (created by the Dartmouth Electron Microscope Facility))

Trees produce 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 have all 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.

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