Types of Allergies 

An allergy starts when your immune system mistakes a normally harmless substance for a dangerous invader. The immune system then produces antibodies that remain on the alert for that particular allergen. When you're exposed to the allergen again, these antibodies can release a number of immune system chemicals, such as histamine, that cause allergy symptoms.

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Common allergies include:

• Airborne allergens, such as pollen, animal dander, dust mites and mold

• Certain foods, particularly peanuts, tree nuts, wheat, soy, fish, shellfish, eggs and milk

• Insect stings, such as from a bee or wasp

• Medications, particularly penicillin or penicillin-based antibiotics

• Latex or other substances you touch, which can cause allergic skin reactions

Risk factors

You might be more likely to develop an allergy if you:

• Have a family history of asthma or allergies, such as hay fever, hives or eczema

• Are a child

• Have asthma or another allergic condition

Complications

Having an allergy increases your risk of certain other medical problems, including:

• Anaphylaxis. If you have severe allergies, you're at increased risk of this serious allergy-induced reaction. Foods, medications and insect stings are the most common triggers of anaphylaxis.

• Asthma. If you have an allergy, you're more likely to have asthma — an immune system reaction that affects the airways and breathing. In many cases, asthma is triggered by exposure to an allergen in the environment (allergy-induced asthma).

• Sinusitis and infections of the ears or lungs. Your risk of getting these conditions is higher if you have hay fever or asthma.