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What Are Allergies?

Allergies are when the body’s immune system, which normally fights infections, overreacts to things that are typically harmless to most people. When you're allergic to something, your immune system thinks it's harmful and releases chemicals like histamine (pronounced: HIS-tuh-meen). (Substances that cause allergic reactions — such as some foods, dust, plant pollen, or medicines — are known as allergens.)

What Happens in Allergies?

To try to protect the body, the immune system makes IgE antibodies to that allergen. Those antibodies then cause certain cells in the body to release chemicals into the bloodstream, one of which is histamine.

These chemicals then act on the eyes, nose, throat, lungs, skin, or gastrointestinal tract and causes the symptoms of the allergic reaction. Future exposure to that allergen will trigger this antibody response again. This means that every time you have contact with that allergen, you'll have some form of allergy symptoms.

What Are the Signs and Symptoms of Allergies?

Allergic reactions can differ. Sometimes the same person can react differently at different times. Some reactions can be very mild and involve only one system of the body, like hives on the skin or a runny nose. Other reactions can be more severe and involve more than one part of the body.

Some allergies can cause a severe reaction called anaphylaxis (pronounced: an-uh-fuh-LAK-sis), even if a previous reaction was mild. Anaphylaxis might start with some of the same symptoms as a less severe reaction, but can quickly get worse. The person may have trouble breathing or pass out. More than one part of the body might be involved. If it isn't treated, anaphylaxis can be life-threatening.

What Causes Allergies?

The tendency to develop allergies often runs in families. But just because a parent or sibling has allergies doesn't mean you will definitely get them too. A person usually doesn't inherit a particular allergy, just the likelihood of having any type of allergy.

What Things Are People Allergic to?

Some of the most common allergies are:

Airborne Allergies

These include:

  • dust mites
  • pollen (often called hay fever)
  • molds
  • pets
  • cockroaches

Food Allergies

These are the top causes of food allergies in teens:

Other Common Allergies

  • insect stings allergy: The venom (poison) in insect stings can cause allergic reactions. These can be severe and even cause an anaphylactic reaction in some people.
  • medicines: Antibiotics (used to treat infections) are the type of medicines that most often cause allergic reactions. Many other medicines, including over-the-counter ones you can buy without a prescription, also can cause allergic reactions.
  • chemicals: Some cosmetics or laundry detergents can make people break out in hives. Usually, this is because someone has a reaction to the chemicals in these products, though it may not always be an allergic reaction. Dyes, household cleaners, and pesticides used on lawns or plants also can cause allergic reactions in some people.

How Are Allergies Diagnosed?

If your doctor thinks you might have an allergy, they might want you to see an allergist (a doctor who diagnoses and treats allergies).

The allergist will ask you about your own allergy symptoms (such as how often they happen and when) and if any family members have allergies. The allergist also will do testing to confirm an allergy. The tests will depend on the type of allergy suspected, and may include a or blood test.

How Are Allergies Treated?

There's no cure for allergies, but symptoms can be managed.

The best way to avoid allergic reactions is to stay away from whatever causes them. This is called avoidance. Doctors can also treat some allergies with medicines and allergy shots.

Tips for Avoiding Allergens

In some cases, as with food allergies, avoiding the allergen is a life-saving necessity. Unlike allergies that can be treated with shots or medicines, the only way avoid reactions from food allergies is to avoid the allergen entirely. For example, people who are allergic to peanuts should avoid not only peanuts, but also any food that might contain even tiny traces of them.

Avoidance can help protect people against non-food or chemical allergens too. In fact, for some people, staying away from an allergen is enough to prevent allergy symptoms and they don't need to take medicines or go through other allergy treatments.

To help you avoid airborne allergens:

  • Keep family pets out of certain rooms, like your bedroom, and have someone else bathe and brush them once a week. (But for some people with serious symptoms, keeping a pet might not be possible.)
  • Remove carpets or rugs from your room (hard floor surfaces don't collect dust as much as carpets do).
  • Don't hang heavy drapes, and get rid of other items that let dust build up.
  • Clean often (if your allergy is severe, you may be able to get someone else to do your dirty work!).
  • Use special covers to seal pillows and mattresses if you're allergic to dust mites.
  • Consider getting an air cleaner with a HEPA (high efficiency particulate air) filter for your bedroom.
  • If you're allergic to pollen, keep windows closed when pollen season is at its peak, change your clothing and shower after being outdoors, and don't mow lawns.
  • If you're allergic to mold, avoid damp areas, such as basements, and keep bathrooms and other mold-prone areas clean and dry.

Allergy Medicines

Medicines (such as pills or nasal sprays) are often used to treat allergies. Although they can control the allergy symptoms (such as sneezing, headaches, or a stuffy nose), they're not a cure and can't make the tendency to have allergic reactions go away.

Many effective medicines are available to treat common allergies, and your doctor can help you find ones that work for you.

Another type of medicine that some severely allergic people will need to carry is epinephrine (pronounced: eh-puh-NEH-frin). This fast-acting medicine can help offset an anaphylactic reaction. It comes in a small and easy to use auto-injector. Epinephrine is available by prescription only. If you have a severe allergy and your doctor thinks you should carry it, they'll give you instructions on how to use it. Always have two auto-injectors with you in case one doesn't work or you need a second dose.

Allergy Shots

Allergy shots are also called allergen immunotherapy. By getting injections of small amounts of an allergen, a person's body can slowly become less sensitive to that allergen.

Immunotherapy is only recommended for specific allergies, such as to things a person can breathe in (like pollen, pet dander, or dust mites) or insect allergies. 

Allergy shots can’t be used to treat some allergies, like food allergies.

Some people might find the thought of allergy shots unsettling, but they can be very effective — and it doesn't take long to get used to them. Often, the longer someone gets allergy shots, the more they help the body build up antibodies that fight the allergies. Although the shots don't cure allergies, they do tend to raise a person's tolerance when exposed to the allergen, which means fewer or less serious symptoms.

If you're severely allergic to insect bites and stings, talk to an allergist about getting venom immunotherapy (shots).

What Can Help Me Deal With Allergies?

So once you know you have allergies, how do you deal with them? First, try to avoid things you're allergic to!

If you have a food allergy, avoid foods that trigger symptoms and read food labels to make sure you're not eating even tiny amounts of allergens. Always carry two epinephrine auto-injectors in case of a reaction.

If you have an environmental allergy, keep your house clean of dust and pet dander and watch the weather forecast for days when pollen is high. Switching to perfume-free and dye-free detergents, cosmetics, and beauty products (you may see non-allergenic ingredients listed as hypoallergenic on product labels) also can help.

If you're taking medicine, follow the label directions carefully and make sure your regular doctor is aware of anything an allergist gives you (like shots or prescriptions). If you have a severe allergy, consider wearing a medical emergency ID (such as a MedicAlert bracelet), which will explain your allergy and who to contact in case of an emergency.

If you've been diagnosed with allergies, you have plenty of company. And the good news is that doctors and scientists are working to better understand allergies, to improve treatments, and to possibly prevent allergies someday.

Medically reviewed by: Larissa Hirsch, MD
Date reviewed: April 2024