Allergies Health Center

What Causes Chronic Allergies?

If you've got allergies, you might wonder what to expect in the long term. Are you stuck with allergy symptoms, or will they get better? Or could they actually get even worse?

Unfortunately, there are no simple answers. A lot remains unknown about how allergies develop, and each person's case is different. But here's a rundown of what we do know.

What Causes Allergies?

If you have allergies, you might blame the allergens -- the pollen in the air, your best friend's cat -- for your symptoms.

But actually, most allergens are themselves harmless innocents. What really causes allergic reactions is your own immune system. It mistakes these innocuous allergens for a serious threat and attacks them. The symptoms of an allergy are the result of a body's misguided assault.

Who Gets Allergies?

Your risk of developing an allergy starts in your genes. While specific allergies are not inherited, a tendency toward having allergies is. Children with one allergic parent have a 33% chance of developing allergies; with two allergic parents, it's a 70% chance.

Just being predisposed isn't enough. Even the most allergy-prone people don't develop allergies to everything. The circumstances have to be just right for a potential allergen to trigger an allergic reaction.

A lot remains mysterious about just what causes allergies to develop. But it does seem that your current health may have an impact. For instance, if you come into contact with an allergen when you're weak -- say, after a viral infection -- you might be more likely to develop an allergy to it.

What Causes Allergies to Start?

It begins with exposure. Even if you've inhaled an allergen many times before with no trouble, at some point, for some reason, the body flags it as an invader. During this particular exposure, the immune system studies the allergen. It readies itself for the next exposure by developing antibodies, special cells designed to detect it. You are now "sensitized" to the allergen.  

Then, the next time you're exposed to the allergen, your immune system kicks into action. The antibodies recognize it. That triggers the activation of special cells called mast cells. These cells are responsible for allergy symptoms in the lungs, skin, and lining of the nose and intestinal tract.

The mast cells burst open, flooding the system with chemicals such as histamine. These chemicals cause allergy symptoms, like swelling. Swelling in your nasal passages might cause a runny nose. Swelling in the airways could cause asthma symptoms.

Keep in mind that the amount of exposure matters. If you're allergic to strawberries, maybe eating one or two never causes any symptoms. But once you eat three or four, you may suddenly break out in hives. There's a tipping point -- or threshold -- for people with allergies. You can handle some exposure, but if it gets to be too much, the immune system is triggered to attack.