While more common in children, allergies can affect people of any age.

Allergies happen when your immune system overreacts to substances called allergens.

Common allergens include pollen, pet dander, and bee venom.

If you have allergies, your body mistakenly identifies an allergen as harmful and tries to destroy it, resulting in unpleasant allergy symptoms.

Allergies can be mild, severe, or — in some cases — life-threatening.

What Is IgE?

When your immune system reacts to an allergen, it produces an antibody called immunoglobulin E (IgE).

The production of IgE is part of your body's attempt to destroy the allergen and protect itself.

But this process allows the IgE antibodies to signal other cells to release certain chemicals, such as histamine.

Too much histamine in the body can cause an unwanted response that leads to skin, nose, throat, and lung irritation.

Who Gets Allergies?

As many as one in five Americans — a total of about 50 million — have some type of allergy, according to the American College of Allergy, Asthma, and Immunology.

Allergies are the sixth most common cause of chronic illness in the United States, with an annual cost of more than $18 billion.

While they can affect anyone, allergies are more common in children than in adults.

The prevalence of food and skin allergies in children has increased in recent years, but experts aren't sure why.

Food allergies affect about 1 in every 13 American kids, according to FARE (Food Allergy Research & Education).

Each year, allergic reactions account for about two million missed school days.

Types of Allergies

There are several different types of allergies. Some are seasonal, and others occur year-round.

The most common allergens that trigger flare-ups include:

• Pollen
• Dust mites
• Pet dander or fur
• Cockroaches
• Mold spores
• Foods (eggs, fish, milk, nuts, wheat, soy, shellfish, and others)
• Insect stings or bites (from wasps, bees, mosquitoes, fire ants, fleas, horseflies, black flies, and others)
• Medicines (penicillin, aspirin, and others)
• Latex
• Household chemicals
• Metals (especially nickel, cobalt, chromium, and zinc)

Risk Factors

Your risk of developing allergies is higher if you:

• Have asthma
• Have a family history of asthma or allergies
• Are a child under age 18

Sometimes, children outgrow allergies as they get older.

It's also common for allergies to go away and then come back years later.

Allergy Complications

If you have severe allergies, you may experience a life-threatening allergic reaction called anaphylaxis.

This condition is most commonly associated with allergies involving food, penicillin, and insect venom.

Symptoms of anaphylaxis may include:

• A drop in blood pressure
• Loss of consciousness
• Severe shortness of breath
• Skin rash
• Rapid or weak pulse
• Nausea or vomiting
• Lightheadedness
• Severe wheezing

If this happens to you or someone around you, call 911 or seek emergency medical help right away.

People with allergies are also at risk of developing complications including:

• Asthma (a respiratory illness that causes narrowing and inflammation of the airways leading to chest tightness, wheezing, and difficulty breathing)
• Eczema (a skin condition characterized by inflammation)
• Ear or lung infections
• Sinusitis or sinus infection
• Nasal polyps (growths on the lining of the nose or sinuses)
• Migraine headaches

Preventing Allergic Reactions

Some measures you can take to prevent or limit allergic reactions include:

Avoiding triggers This may be difficult, depending on the allergen you're trying to dodge.

For example, if you're allergic to pet dander, stay away from animals. If you're allergic to pollen, try remaining indoors when pollen counts are high.

Keeping a diary If you're trying to figure out which allergens might cause or worsen your symptoms, write down what you eat and all of your activities to help pinpoint triggers.

Wearing a medical alert bracelet or necklace These can let others know that you have a serious allergy if you aren't able to communicate during a severe allergic reaction.

For some people with severe allergies, however, it's necessary to have epinephrine immediately available in case anaphylaxis occurs.

Ask your doctor if this is necessary for you.

Sources

• Allergies; American College of Allergy, Asthma & Immunology.
• Allergies; Mayo Clinic.
• Allergy; MedlinePlus.
• E. R. Shell (2015). "An Overreaction to Food Allergies." Scientific American.
• All About Allergies; KidsHealth.