Allergies occur when your immune system reacts to a foreign substance — such as pollen, bee venom or pet dander — or a food that doesn't cause a reaction in most people.

Your immune system produces substances known as antibodies. When you have allergies, your immune system makes antibodies that identify a particular allergen as harmful, even though it isn't. When you come into contact with the allergen, your immune system's reaction can inflame your skin, sinuses, airways or digestive system.

The severity of allergies varies from person to person and can range from minor irritation to anaphylaxis — a potentially life-threatening emergency. While most allergies can't be cured, treatments can help relieve your allergy symptoms.

Certain foods

Food allergies develop when your body releases a specific antibody to a particular food. An allergic reaction occurs within minutes of eating the food, and symptoms can be severe. Symptoms may include:

• Itching all over your body (generalized pruritus).

• Itching in just one certain part of your body (localized pruritus).

• Nausea and vomiting.

• Hives.

• Swelling around your mouth, including your throat, tongue or face.

If you have an IgE-mediated food allergy, symptoms may also include anaphylaxis. It may present as any one of the above symptoms or a combination of the above symptoms. It usually occurs within 30 minutes of ingesting a food you’re allergic to.

In adults, the most common food allergies are:

• Milk.

• Eggs.

• Wheat.

• Soy.

• Peanuts.

• Tree nuts.

• Shellfish.

In children, the most common food allergies are:

• Milk.

• Eggs.

• Wheat.

• Soy.

• Peanuts

• Tree nuts.

Inhalants

Inhalant allergies are airborne substances that you inhale (breathe in). They include allergens that may affect you throughout the year (perennial allergens) and seasonal allergens.

Inhalant allergy symptoms include:

• Runny nose.

• Stuffy nose.

• Itchy nose.

• Sneezing.

• Itchy eyes.

• Watery eyes.

If you have asthma, inhalant allergies can also trigger or worsen your symptoms, including wheezing and shortness of breath.

Perennial allergens include:

• Pets. Pet allergens include certain proteins in animal fur, skin (dander), urine (pee) and saliva (spit).

• Dust mites. Dust mites are tiny, eight-legged relatives of spiders. They’re too small to see with your eyes. They live in dust and the fibers of household objects, such as pillows, mattresses, carpets and upholstery.

• Cockroaches. Cockroaches are reddish-brown insects that are 1.5 to 2 inches (in) long. The proteins in their feces (poop), spit, eggs and dead body parts can cause allergic reactions.

• Molds. Molds are tiny fungi (plural of fungus). They have spores that float in the air, like pollen. Common mold allergies include Aspergillus, Cladosporium and Alternaria.

Seasonal allergies include pollens. Pollen is microspores from trees, grass or weeds that appear as a fine dust on surfaces or float in the air. Tree pollens generally appear in the spring, while weed pollens generally appear in the fall.