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What causes chronic allergies?

Having an allergy may be inherited through a person's genes, but environment and other factors play a part.

Everyone's allergy triggers and symptoms will be different because of the way their immune system responds to any allergens it detects.

It mistakes things like pollen and pet dander as a serious threat and attacks them. The symptoms of an allergy are the result of your body's defences.

Who gets allergies?

Your risk of developing an allergy starts in your genes. While specific allergies are not inherited, a tendency towards having allergies is. Children with one allergic parent have a 33% chance of developing allergies.

Just being predisposed isn't enough. Even the most allergy-prone people don't develop allergies to everything. The circumstances have to be exactly 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 - for example, 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 without trouble, at some point, for some reason, your body flags it as an invader. During this particular exposure, the immune system studies the allergen. It prepares itself for the next exposure by developing antibodies, special cells designed to detect it. You are now "sensitised" to the allergen.  

Then, the next time you're exposed to the allergen, your immune system kicks into action. The antibodies recognise 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 your system with chemicals such as histamine that cause allergy symptoms, like swelling. Swelling in your nasal passages might cause a runny nose. Swelling in your 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, your immune system is triggered to attack.

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