What causes allergies?

By: Karen Serrano, MD

Causes of Nasal Allergy

  • Nasal allergies are an exaggerated response of the immune system to usually harmless substances.
  • You may inherit a tendency for allergic reactions.
  • It may take many exposures over a long period of time to develop an allergic reaction to a particular substance.
  • Factors that may contribute to nasal allergies include: exposure to cigarette smoke, being a low-birth-weight baby, being a bottle-fed baby, being born during high-pollen seasons.

What Happens When Nasal Allergies Flare

No one knows why some people are allergic to substances such as pollens or dust mites and others aren't. Many experts believe that people inherit sensitivity to 1 or more allergens, and most assume there are differences in people's immune systems that make them ultrasensitive. What is known is that anyone can develop nasal allergies at any age.

Role of the Immune System in Allergies

Every day, your body is exposed to millions of bacteria, viruses, and other potentially harmful microscopic invaders. Your body's immune system normally defends you from illness. It works hard to kill these invaders before they can harm you. Occasionally, a virus or other germ gets by your immune system, and you get sick. But unless something is seriously wrong with your immune system, your body usually wards off these attacks.


Sometimes, though, your body's defense system goes haywire. When you have nasal allergies and an allergen gets into your body, your immune system believes it is under attack, so it launches a defense. Your body releases powerful chemicals called histamine from cells in your body called mast cells and basophils. Histamine is what makes your nose run and your eyes water. It makes you sneeze and wheeze. It may even cause problems breathing. This is an allergic reaction.

When your body responds this way, it is responding to a false alarm. Unfortunately, you pay the price with miserable allergy symptoms.

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Written by Karen Serrano, MD Emergency Medicine resident at the University of Wisconsin-Madison.

Reviewed by Lisa V. Suffian, MD

Instructor of Clinical Pediatrics in the Division of Allergy and Pulmonary Medicine at Saint Louis Children's Hospital, Washington University School of Medicine

Assistant Clinical Professor in the Department of Pediatrics at Cardinal Glennon Children's Hospital, Saint Louis University

Board certified in Allergy and Immunology

Last updated June 2008