Slideshow Pictures: Allergy -- What Happens in a Nasal Allergy Attack

Allergy Causes

Allergy triggers can be anywhere. Pollen, ragweed, grass, pet dander, dust mites, and mold are some of the most common allergens. People who have allergies have an immune system that is sensitive to one or more of these usually harmless substances.

Allergens: The Invader

Normally your immune system targets and protects you against threats like viruses and bacteria. Here you can see some bacteria (pink) being surrounded. But if you're allergic to pollen, for example, your immune system sees pollen as a threat. So when you're exposed to pollen, your immune system is ready to fight.

What Triggers an Allergy

It’s easy to come in contact with allergens. Chasing after dust bunnies, playing with your pet, or just walking out the door during allergy season can do it. An allergic reaction is set in motion by touching, swallowing, or inhaling an allergen.

Your Immune System Reacts

Pollen (magnified above) can get caught in the lining of your nose and trachea, or windpipe. Once an allergen, such as pollen, enters your body, your immune system reacts and starts making antibodies that help look for and then get rid of the pollen.

Allergic Response: Histamine Release

When antibodies find an allergen, they alert mast cells. These specialized blood cells release chemicals such as histamine, which plays a key role in inflammation and allergy symptoms. A runny nose, swelling in the nasal passages, and congestion can result.

What Causes Allergies?

Allergies tend to run in families. Having a parent with allergies or asthma puts you at greater risk. When one parent has allergies, about 25% of the time the child will develop them, too. When both parents are allergic, that risk at least doubles. What you develop an allergy to also depends on your exposure to triggers. Some allergies can take years to develop.

Preventing Allergies

Avoid triggers when possible to prevent allergy attacks. That may mean checking pollen or mold reports before heading outside. If levels are high, consider wearing a mask. During allergy season, showering before going to bed helps you avoid sleeping with pollen trapped in your hair. Also keep windows closed and run the air conditioner. Vacuuming twice a week can help cut down on allergens.

Treating Allergies

Over-the-counter medications such as antihistamines, decongestants, eye drops, and nasal sprays also may help control symptoms and provide allergy relief. Talk with your pharmacist or doctor about which might help you.

When to See an Allergist

If you don't know what's causing your allergies, or if they're severe, an allergy doctor can help. An allergist or immunologist will take your medical history and may perform allergy tests. One type -- a patch test -- is shown here. Tests expose you to possible allergens to see which ones cause a reaction. Depending on your allergies, prescription medications or immunotherapy (allergy shots) may be recommended.

More Reading on Allergies

• Hay Fever
• Allergic Reaction

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• Nasal Allergy Relief: Products That Work
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• Common Allergy Triggers
• Signs Your Allergies Are Out of Control
• Pets and Allergies