Hay fever - More about hay fever

Hay fever

More about what happens in hay fever

If you have hay fever, this is what happens.

When you breathe in pollen or mold spores, your

immune system
The immune system is made up of the parts of the body that are devoted to fighting infection. The body is constantly being threatened by infections from things like bacteria, viruses and parasites. The immune system fights these infections in different ways. At the microscopic level, the immune system uses antibodies and white blood cells, which travel in the blood and target infectious agents, such as bacteria. These microscopic parts of the immune system either kill the infectious agent directly, or take it to other parts of the body, like the spleen, where it can be dealt with. The lymph nodes are another important part of the immune system. Within them, white blood cells filter through the foreign material that has entered the blood, to see if there are any infections. When you have a swollen gland during a cold, this is actually a lymph node that is reacting to the infection. Unfortunately, it is possible for the immune system to become confused and to use its destructive powers to target healthy parts of the body. Diseases that result from this type of situation are called autoimmune diseases.

immune system makes a mistake. It reacts as if these things are trying to make you sick.

Source:
U.S. National Institutes of Health.
Understanding cancer series: the immune system.
September 2006. Available at http://www.cancer.gov/ (accessed on 2 July 2008).

¹
This causes special immune cells to release large amounts of an

antibodies
Antibodies are an important part of your immune system. They are proteins made by white blood cells (another part of your immune system). They help destroy bacteria and other agents that cause infections.

antibody called immunoglobulin E (or IgE for short).
This antibody makes your body release large amounts of powerful chemicals. The main ones are histamine, and different cytokines and leukotrienes.
These chemicals make the lining of your nose and the back of your throat irritated and swollen. So your nose and throat make lots of watery mucus.
The chemicals give you the common symptoms of hay fever, such as sneezing, a runny or stuffy nose, and itchy, red eyes. If your lungs are affected, you may get a cough or wheeze.
When your body reacts this way, doctors say you're having an

allergic reaction
You have an allergic reaction when your immune system reacts to something outside your body that is normally harmless. You can be allergic to particles in the air, like pollen, which causes hay fever, or to chemicals, like detergents, which can cause a rash. People can also have an allergic reaction to drugs, like penicillin.

allergic reaction. You can get a reaction like this quite suddenly.

Source:
National Institute of Allergy and Infectious Diseases (NIAID). NIH.
Something in the air: airborne allergens.
April 2003. Available at http://www.niaid.nih.gov (accessed on 2 July 2008).

² Doctors call the thing that makes your immune system react when it doesn't need to an

allergen
If you have an allergy to something, your body overreacts when you're around it. The thing you are allergic to is called an allergen. Most allergens are harmless to most people. But if you're allergic to something, your body's system for fighting infection (your immune system) is too sensitive to that allergen. It triggers changes that we call allergic reactions. For example, pollen is an allergen for many people. If you're allergic to pollen, you'll sneeze and have runny eyes when pollen is in the air.

allergen. So for hay fever, pollen or mold spores are the allergens.

Sources for the information on this page:

U.S. National Institutes of Health.Understanding cancer series: the immune system.September 2006. Available at http://www.cancer.gov/ (accessed on 2 July 2008).

National Institute of Allergy and Infectious Diseases (NIAID). NIH.Something in the air: airborne allergens.April 2003. Available at http://www.niaid.nih.gov (accessed on 2 July 2008).

This information was last updated on May 01, 2009

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