Allergic Rhinitis | Causes & Risk Factors

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What causes allergies?

You have an allergy when your body overreacts to things that don't cause problems for most people. These things are called allergens. If you have allergies, when you are exposed to an allergen, your body releases chemicals. One type of chemical that your body releases is called histamine. Histamine is your body’s defense against the allergen. The release of histamine causes your symptoms.

What are the most common allergens?

Pollen from trees, grass and weeds. Allergies that occur in the spring (late April and May) are often due to tree pollen. Allergies that occur in the summer (late May to mid-July) are often due to grass and weed pollen. Allergies that occur in the fall (late August to the first frost) are often due to ragweed. If you are allergic to pollen, you will notice your symptoms are worse on hot, dry days when wind carries the pollen. On rainy days, pollen often is washed to the ground, which means you are less likely to breathe it.

Mold. Mold is common where water tends to collect, such as shower curtains, window moldings and damp basements. It can also be found in rotting logs, hay, mulches, commercial peat moss, compost piles and leaf litter. This allergy is usually worse during humid and rainy weather.

Animal dander. Proteins found in the skin, saliva, and urine of furry pets such as cats and dogs are allergens. You can be exposed to dander when handling an animal or from house dust that contains dander.

Dust. Many allergens, including dust mites, are in dust. Dust mites are tiny living creatures found in bedding, mattresses, carpeting and upholstered furniture. They live on dead skin cells and other things found in house dust.

Written by familydoctor.org editorial staff

Reviewed/Updated: 04/14
Created: 01/96

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