Allergies - overview

  • Definition
    • An allergy is an immune response or reaction to substances that are usually not harmful.

      Seasonal Allergy Facts

      1. What causes seasonal allergies?

        1. A. Not spending enough time outdoors
        2. B. Spending too much time outdoors
        3. C. An immune system reaction

        The correct answer is an immune system reaction. Your immune system normally protects your body against harmful bacteria and viruses. If you have seasonal allergies, this system reacts strongly to harmless pollens. Seasonal allergies are also sometimes called hay fever.

      2. What are common seasonal allergy symptoms?

        1. A. Itchy nose, mouth, eyes, throat, skin, or any area
        2. B. Problems with smell
        3. C. Runny nose
        4. D. Sneezing
        5. E. Tearing eyes
        6. F. All of the above

        The correct answer is all of the above. When you come in contact with an allergy trigger, your body releases the chemical histamine. This causes allergy symptoms. Other symptoms include cough, sore throat, puffy eyes, tiredness, and headache. Tell your doctor if you notice allergy symptoms.

      3. What else can cause allergy symptoms in some people?

        1. A. Dust mites
        2. B. Pet dander (dead skin that sheds)
        3. C. Mold
        4. D. A and B
        5. E. A, B, and C

        The correct answer is A, B, and C. These triggers create symptoms that affect the nose. It's not always easy to know what is causing allergy symptoms. If you start sneezing and your nose runs, write down what you were doing when symptoms started. Learning what causes your symptoms can help you avoid allergy triggers.

      4. Your doctor can do tests to find out what causes your allergies.

        1. A. True
        2. B. False

        The correct answer is true. Your doctor can test you to see what causes an allergic reaction. The most common is a skin prick test. A small amount of a possible allergy trigger is placed on your skin. Then the skin is gently pricked to allow it to go under the skin. If you have swelling or redness, you are allergic.

      5. What can you do to avoid allergy triggers?

        1. A. Reduce dust and dust mites in the home.
        2. B. Control molds indoors and out.
        3. C. Learn when pollen counts are high and avoid being outdoors.
        4. D. Never go outside and get rid of your pets.
        5. E. A, B, and C.

        The correct answer is A, B, and C. To reduce allergy triggers in your home, install furnace filters or other air filters. Use a dehumidifier to dry the air in your house and prevent mold. If you have pets, don't let them in your bedroom or on furniture. Pay attention to pollen levels in your area, and avoid going outside when levels are high.

      6. What produces the pollen that causes allergies?

        1. A. Trees that produce pollen in the spring
        2. B. Grasses that produce pollen during the late spring and summer
        3. C. Ragweed and other late-blooming plants that produce pollen in late summer and early autumn
        4. D. All of the above

        The correct answer is all of the above. If you get seasonal allergies, work with your doctor to find out what you are allergic to.

      7. Pollen levels are highest on cool, damp, rainy days.

        1. A. True
        2. B. False

        The correct answer is false. More pollen is in the air on hot, dry, windy days. The amount of pollen in the air can affect whether hay fever symptoms develop. Check for pollen count in your area in the news or online. Stay indoors in air conditioning if possible when counts are high.

      8. Which can treat allergies?

        1. A. Eye drops
        2. B. Pills
        3. C. Injections
        4. D. Nasal sprays
        5. E. All of the above

        The correct answer is all of the above. Common medicines include antihistamines, corticosteroids, and decongestants. Treatments are available over-the-counter and by prescription. Your doctor will recommend a medicine based on what you are allergic to and how severe your allergies are.

      9. Allergy shots can treat severe seasonal allergies.

        1. A. True
        2. B. False

        The correct answer is true. Your doctor may recommend shots if you can't avoid allergy triggers and your symptoms are hard to control. You will get regular shots of the substance that causes the reaction. Allergy shots help your body adjust and stop reacting to the allergy trigger. Ask your doctor if this therapy is right for you.

  • Alternative Names
    • Allergy - allergies; Allergy - allergens

  • Causes
    • Allergies are very common. Both genes and environment play a role. If both your parents have allergies, there is a good chance that you have them, too.

      The immune system normally protects the body against harmful substances, such as bacteria and viruses. It also reacts to foreign substances called allergens. These are usually harmless and in most people do not cause a problem.

      Allergic reactions

      In a person with allergies, the immune response is oversensitive. When it recognizes an allergen, the immune system launches a response. Chemicals such as histamines are released. These chemicals cause allergy symptoms.


      Common allergens include:

      • Drugs
      • Dust
      • Food
      • Insect venom
      • Mold
      • Pet and other animal dander
      • Pollen

      Some people have allergy-like reactions to hot or cold temperatures, sunlight, or other environmental triggers. Sometimes, friction (rubbing or roughly stroking the skin) will cause symptoms.

      Allergies may make certain medical conditions, such as sinus problems, eczema, and asthma, worse.

  • Symptoms
    • Mostly, the part of the body the allergen touches affects what symptoms you develop. For example:

      At times, an allergy can trigger a response that involves the entire body.

      Hives (urticaria) on the chest
  • Exams and Tests
    • The health care provider will perform a physical exam and ask questions, such as when the allergy occurs.

      Allergy testing may be needed to find out whether the symptoms are an actual allergy or are caused by other problems. For example, eating contaminated food (food poisoning) may cause symptoms similar to food allergies. Some medicines (such as aspirin and ampicillin) can produce non-allergic reactions, including rashes. A runny nose or cough may actually be due to an infection.

      Skin testing is the most common method of allergy testing:

      • The prick test involves placing a small amount of the suspected allergy-causing substances on the skin, and then slightly pricking the area so the substance moves under the skin. The skin is closely watched for signs of a reaction, which include swelling and redness.
      • The patch test involves placing a patch with the suspected allergen on your skin. The skin is then closely watched for signs of a reaction.
      • The intradermal test involves injecting tiny amount of allergen under your skin, then watching the skin for a reaction.

      The doctor may also check your reaction to physical triggers by applying heat, cold, or other stimulation to your body and watching for an allergic response.

      Blood tests that may be done include:

      In some cases, the doctor may tell you to avoid certain items to see if you get better, or to use suspected items to see if you feel worse. This is called "use or elimination testing." This is often used to check for food or medicine allergies.

  • Treatment
    • Severe allergic reactions (anaphylaxis) need to be treated with a medicine called epinephrine. It can be life-saving when given right away. If you use epinephrine, call 911 and go straight to the hospital.

      The best way to reduce symptoms is to avoid what causes your allergies. This is especially important for food and drug allergies.

      There are several types of medicines to prevent and treat allergies. Which medicine your doctor recommends depends on the type and severity of your symptoms, your age, and overall health.

      Illnesses that are caused by allergies (such as asthma, hay fever, and eczema) may need other treatments.

      Introduction to allergy treatment

      Medicines that can be used to treat allergies include:


      Antihistamines are available over-the-counter and by prescription. They are available in many forms, including:

      • Capsules and pills
      • Eye drops
      • Injection
      • Liquid
      • Nasal spray


      These are anti-inflammatory medicines. They are available in many forms, including:

      • Creams and ointment for the skin
      • Eye drops
      • Nasal spray
      • Lung inhaler
      • Pills
      • Injection

      Persons with severe allergic symptoms may be prescribed corticosteroid pills or injections for short periods.


      Decongestants help relieve a stuffy nose. Do not use decongestant nasal spray for more than several days because they can cause a rebound effect and make the congestion worse. Decongestants in pill form do not cause this problem. People with high blood pressure, heart problems, or prostate enlargement should use decongestants with caution.


      Leukotriene inhibitors are medicines that block the substances that trigger allergies. Person with asthma and indoor and outdoor allergies may be prescribed these medicines.


      Allergy shots (immunotherapy) are sometimes recommended if you cannot avoid the allergen and your symptoms are hard to control. Allergy shots keep your body from over-reacting to the allergen. You will get regular injections of the allergen. Each dose is slightly larger than the last dose until a maximum dose is reached. These shots do not work for everybody and you will have to visit the doctor often.


      Instead of shots, medicine put under the tongue may help for grass and ragweed allergies.

  • Support Groups
  • Outlook (Prognosis)
    • Most allergies can be easily treated with medicine.

      Some children may outgrow an allergy, especially food allergies. But once a substance has triggered an allergic reaction, it usually continues to affect the person.

      Allergy shots are most effective when used to treat hay fever and insect sting allergies. They are not used to treat food allergies because of the danger of a severe reaction.

      Allergy shots may need years of treatment, but they work in most cases. However, they may cause uncomfortable side effects (such as hives and rash) and dangerous outcomes (such as anaphylaxis). Talk with your provider whether allergy drops (SLIT) are right for you.

  • Possible Complications
    • Complications that may result from allergies or their treatment include:

      • Anaphylaxis (life-threatening allergic reaction)
      • Breathing problems and discomfort during the allergic reaction
      • Drowsiness and other side effects of medicines
  • When to Contact a Medical Professional
    • Call for an appointment with your provider if:

      • Severe symptoms of allergy occur
      • Treatment for allergies no longer works
  • Prevention
    • Breastfeeding can help prevent or decrease allergies when you feed babies this way only for 4 to 6 months. However, changing a mother's diet during pregnancy or while breastfeeding does not seem to help prevent allergies.

      For most children, changing the diet or using special formulas does not seem to prevent allergies. If a parent, brother, sister, or other family member has a history of eczema and allergies, discuss feeding with your child's doctor.

      There is also evidence that being exposed to certain allergens (such as dust mites and cat dander) in the first year of life may prevent some allergies. This is called the "hygiene hypothesis." It came from the observation that infants on farms tend to have fewer allergies than those who grow up in more sterile environments. However, older children do not seem to benefit.

      Once allergies have developed, treating the allergies and carefully avoiding allergy triggers can prevent reactions in the future.

  • References
    • Chiriac AM, Bousquet J, Demoly P. In vivo methods for the study and diagnosis of allergy. In: Adkinson NF Jr, Bochner BS, Burks AW, et al, eds. Middleton's Allergy: Principles and Practice. 8th ed. Philadelphia, PA: Elsevier Saunders; 2014:chap 70.

      Wasserman SI. Approach to the patient with allergic or immunologic disease. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 249.