Give Online: Help shape patient care for generations to come.
Cleveland Clinic Logo

Diseases & Conditions

Allergy Overview

What are allergies?

Allergies are your body's reaction to a substance it views as a harmful “invader.” For example, coming into contact with what is normally a harmless substance, such as pollen, might cause the immune system (the body's defense system) to react. Substances that cause these reactions are called allergens.

What is an allergic reaction?

An “allergic reaction” is way the body responds to the allergen. A chain of events occur that result in an allergic reaction.

The first time an allergy-prone person is exposed to a specific allergen (such as pollen), the body responds by producing allergic (IgE) antibodies. The job of these antibodies is to find molecules of the offending substance in the bloodstream and tissues and to usher them to the body's mast cells (a type of white blood cell) for destruction. As the mast cells destroy the allergens, a chemical called histamine is released into the bloodstream. A large amount of histamine swells body tissues (inflammation), causes itching, enlarges blood vessels, increases secretions, and causes bronchospasm (tightening of muscles that surround the airways).

What are the symptoms of allergies?

Allergy symptoms can be classified as mild, moderate, or severe:

  • Mild reactions include local symptoms (affecting a specific area of the body) such as a rash or hives; itchiness, watery/red eyes, hay fever, and runny nose. Mild reactions do not spread to other parts of the body.
  • Moderate reactions include symptoms that spread to other parts of the body. Symptoms may include itchiness, hives, and/or swelling, and trouble breathing.
  • A severe allergic reaction, known as anaphylaxis, is a rare, life-threatening emergency in which the body's response to the allergen is sudden and affects the whole body. Anaphylaxis may begin with severe itching of the eyes or face. Within minutes, more serious symptoms appear, including throat swelling (which could cause problems with swallowing and breathing); abdominal pain; cramps; vomiting; diarrhea; hives; and swelling (angioedema). The person may also have mental confusion or dizziness, since anaphylaxis may cause a drop in blood pressure.

What are the types of allergies and how are they treated?

People can be allergic to a wide variety of substances; the most common are pollen and dust mites. Other airborne allergens include molds and animal dander.


Seasonal allergic rhinitis, or hay fever, is an allergic response to pollen. It causes inflammation and swelling of the lining of the nose and of the protective tissue of the eyes (conjunctiva).

Symptoms include sneezing, congestion (feeling stuffy), and itchy, watery eyes. Treatment options include over-the-counter and prescription antihistamines, anti-leukotrienes, nasal steroids, and nasal cromolyn. Some people may have allergic asthma symptoms (wheezing, shortness of breath, chest tightness) caused by exposure to pollen.

Symptoms can be reduced by avoiding pollen. Stay indoors when pollen counts are high, close windows, and use air conditioning. Immunotherapy (“allergy shots”) also may be used to treat pollen allergy.

Dust mites

Dust mites are tiny organisms that live in dust and in the fibers of household objects, such as pillows, mattresses, carpet, and upholstery. Dust mites especially love warm, humid areas.

The symptoms of dust mite allergy are similar to those of pollen allergy. To help manage dust mite allergies, try using dust mite encasements (airtight plastic/polyurethane covers) over pillows, mattresses, and box springs. Also, remove carpet, or vacuum frequently with a high-efficiency filter vacuum cleaner. Treatment may include medications to control nasal/eye and chest symptoms. Immunotherapy may be recommended for people whose symptoms are not adequately controlled with avoidance methods and medications.


Molds are parasitic, tiny fungi (like Penicillium) with spores that float in the air like pollen. Mold is a common trigger for allergies. Mold can be found indoors in damp areas, such as the basement or bathroom, as well as outdoors in grass, leaf piles, hay, mulch, or under mushrooms. Mold spores reach a peak during hot, humid weather.

Treatment may include medications to control nasal/eye and chest symptoms. Immunotherapy may be recommended for people whose symptoms are not adequately controlled with avoidance and medications.

Animal dander

Allergic reactions can be caused by the proteins secreted by sweat glands in an animal's skin, which are shed in dander, and (to a lesser extent) by the proteins in an animal's saliva. Avoidance measures don’t work as well as simply removing the pet from the home. However, because many people are reluctant to do this, second-best measures include keeping the pet out of the bedroom, using air cleaners with HEPA filtration, and washing the pet (cat or dog) frequently.

Treatment may include medications to control nasal/eye and chest symptoms. Immunotherapy may be recommended for people whose symptoms are not adequately controlled with avoidance methods and medications.

Other allergens include:


Some people can develop a latex allergy after repeated contact with latex. Rubber gloves, such as those used in surgery or home cleaning, are a major source for causing this type of reaction. Skin rash, hives, eye tearing and irritation, wheezing, and itching of the skin may occur in people with latex allergy.

Allergic reactions to latex can be mild, such as skin redness and itching. More severe reactions can occur if the mucosal membranes are exposed, such as during an operation or a dental or gynecologic exam.

Treatment of latex reactions begins by removing the offending latex product. If you have latex allergy, it is important for you to wear a Medic Alert bracelet and carry an emergency epinephrine kit. All procedures should be carried out in a “latex-safe” fashion. There is no cure for latex allergy, so the best treatment for this condition is prevention.

Certain foods

Food allergies develop when the body develops a specific antibody to a specific food. An allergic reaction occurs within minutes of eating the food, and symptoms can be severe. In adults, the most common food allergies are shellfish, peanuts, and tree nuts; in children, it’s milk, egg, soy, wheat, shellfish, peanuts, and tree nuts.

Symptoms of food allergy include itching, hives, nausea, vomiting, diarrhea, breathing difficulties, and swelling around the mouth.

The only treatment is to avoid the foods that cause allergy symptoms. If you (or your child) have food allergy, your doctor may prescribe injectable epinephrine (adrenaline) for you to carry at all times. This is necessary in case foods that cause allergies are accidently eaten.

Insect venom (stings)

In a bee sting, the bee usually injects a sac of venom and may leave a stinger in the victim's skin. If the stinger is still in the skin, gently scrape it out with a fingernail or a stiff-edged object like a credit card. Do not pull on the stinger, as this will cause the release of more venom into the skin.

A normal reaction will result in pain, swelling, and redness around the sting site. A large, local reaction may occur that will result in swelling that extends beyond the sting site. For example, a person stung on the ankle may have swelling of the leg.

The most serious reaction to an insect sting is an allergic one, which needs immediate medical attention. Symptoms of an allergic reaction to an insect sting include:

  • Difficulty breathing
  • Generalized (widespread) hives that appear as a red, itchy rash that spreads to areas other than the area that was stung
  • Swelling of the face, throat, or mouth tissue
  • Wheezing or difficulty swallowing
  • Restlessness and anxiety
  • Rapid pulse
  • Dizziness or a sharp drop in blood pressure.

If the patient has a reaction like this, a re-sting can cause a serious reaction that can be life-threatening.

An allergic reaction is treated with epinephrine (adrenaline). Anyone who has had allergic reactions from bee stings should be seen by a board-certified allergy/immunology doctor to confirm by skin and/or blood testing to bee venom that they have an allergy. Venom immunotherapy is recommended when venom allergy is confirmed. This will help reduce the possibility that a re-sting will cause a serious reaction.

What is allergic rhinitis?

Nasal allergy symptoms and hay fever are referred to as “allergic rhinitis.” Seasonal allergic rhinitis is nasal allergies that change with the seasons because of pollen from plants (trees, grasses, or weeds). Seasonal symptoms arise during the pollinating seasons for particular plants. Because you can be allergic to more than one thing, your symptoms may get worse at different times throughout the year, or may be constant.

Does everyone get allergies?

No. Most allergies are inherited, which means they are passed on to children by their parents. People inherit a tendency to be allergic, although not to any specific allergen. If a child develops an allergy, it is very likely that at least one of his or her parents has allergies.

How common are allergies?

More than 50 million Americans (1 in 6) suffer from all types of allergies, including indoor/outdoor allergies, food and drug, latex, insect, skin and eye allergies. The number of people who have allergies continues to increase across all ages, sex, and racial groups.

How are allergies diagnosed?

If you think you have allergies, don't wait to see if your symptoms will go away. When your symptoms last longer than a week or two and tend to come back, make an appointment with an allergy/immunology specialist.

Allergy skin testing may be used to identify the allergens that are causing your allergy symptoms. The test is performed by pricking your skin with an extract of an allergen, and then checking the skin's reaction.

If a skin test cannot be performed, a radioallergosorbent blood test (RAST) may be taken. This test is not as sensitive as a skin test. The RAST evaluates the number of antibodies produced by the immune system. Higher levels of certain antibodies can identify particular allergies.

How are allergies treated?

Although avoiding the allergen is an important treatment approach, it usually does not completely end the allergic reaction.

Medications such as antihistamines (e.g., Allegra®, Zyrtec®), decongestants (eg, Sudafed®, Contact®), or a combination of over-the-counter and prescription medications, are used to treat allergy symptoms. Nasal sprays such as topical nasal steroids (e.g., Flonase®, Nasonex®), cromolyn sodium, and topical nasal antihistamines also can be used to treat allergy symptoms.

Asthma medications, which reduce allergy symptoms, include:

  • Inhaled bronchodilators
  • Inhaled steroids
  • Oral bronchodilators (theophylline)
  • Oral anti-leukotrienes (Singulair [montelukast], zafirlukast [Accolate®] and zyflo [Zileuton®]), and
  • Injected medications, including an antibody such as omalizumab (Xolair®).

Immunotherapy (“allergy shot therapy”) or allergy oral immunotherapy is recommended for symptoms that are not adequately controlled with a combination of avoidance measures and regular medication use. This shot has been shown to be effective in properly selected patients with allergic rhinitis and/or allergic asthma.

Another treatment option is saline irrigation using a sinus rinse kit. These rinse kits (e.g., Neilmed) are sold over-the-counter or can be made at home. To make your own rinse, combine one-half teaspoon non-iodinated salt with one-half teaspoon baking soda in 8 ounces of distilled or boiled water. This mixture rinses out allergens and decreases the amount of inflammation (edema) they cause.

Can allergies be cured?

Allergies cannot be cured, but symptoms can be controlled using a combination of avoidance measures and medications, as well as allergen immunotherapy in properly selected cases.


© Copyright 1995-2016 The Cleveland Clinic Foundation. All rights reserved.

Can't find the health information you’re looking for?

This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 3/9/2016…#8610