Allergies happen when your immune system reacts to a foreign substance, such as pollen, food, or pet dander. Symptoms of allergies include minor irritations to life-threatening reactions.

Allergies Overview

Reviewed: May 8, 2014

Allergies are very common and affect millions of Americans.

Allergies occur when the body's immune system reacts to an allergen. The reaction is called “hypersensitivity” and causes the body to release inflammatory proteins into the body. Allergens are any foreign substance that triggers the body's immune system to react defensively. Allergens include substances such as pollen, dust, pet dander, insect venom, mold, certain medications, and various foods.

Symptoms of an allergy or hypersensitivity reaction range from mild irritations such as sneezing, coughing, skin irritations, and a runny nose to more serious reactions such as indigestion, vomiting, and diarrhea. In some cases, an extreme, life-threatening reaction called anaphylaxis can occur in response to allergens; anaphylaxis can cause a patient's airway to swell and close, which prevents the person from breathing.

There is no specific cause of allergies. Family history, genetics, and environmental exposure to allergens all contribute to the risk of developing allergies.

Allergies cannot be completely cured, but there are treatments available to manage them and actions that can be taken to prevent reactions. Prescription and non-prescriptions medications, including antihistamines, are used to treat seasonal and pollen allergies. Long-term treatment of other allergies may require immunotherapy to allow the body to increase its tolerance to an allergen over time.

Allergies Symptoms

Symptoms of allergies depend on the allergen and can affect the airways, sinuses, nasal passages, skin, and digestive system. Hypersensitivity reactions to allergens range from mild symptoms to severe, life-threatening reactions. Some types of allergies can cause a severe reaction known as anaphylaxis. This is a life-threatening medical emergency and requires immediate medical attention. Signs and symptoms of anaphylaxis include:

  • Loss of consciousness
  • Decreased blood pressure
  • Severe shortness of breath
  • Skin rash
  • Lightheadedness
  • A rapid, weak pulse
  • Nausea and vomiting

Common symptoms of an allergy to pollen include:

  • Sneezing
  • Itching of the nose, eyes, or roof of the mouth
  • Runny or stuffy nose
  • Watery, red, or swollen eyes

Common symptoms of an allergy to a food include:

  • Tingling mouth
  • Swelling of the lips, tongue, face, or throat
  • Hives
  • Anaphylaxis

Common symptoms of an allergy to insect venom include:

  • Swelling at the site of the insect sting or bite
  • Itching or hives all over the body
  • Coughing, wheezing, chest tightness or shortness of breath
  • Analphylaxis

Common symptoms of an allergy to a drug include:

  • Hives
  • Itching skin
  • Rash
  • Swelling of the lips, tongue, face, or throat
  • Wheezing or difficulty breathing
  • Anaphylaxis

Allergies Causes

Allergies and hypersensitivity reactions are caused when the body's immune system release inflammatory proteins in response to an allergen. Since immune systems vary from person to person, allergies and allergic reactions differ greatly among individuals.One person's immune system may attack the allergen bee venom and another's may react to peanut ingestion.

An allergy starts when your immune system mistakes a normally harmless substance for a dangerous substance. The immune system then produces antibodies that remain alert for another exposure to that particular allergen. When you are exposed to the allergen again, these antibodies release immune system chemicals, such as histamine, that cause allergy symptoms.

The cause of allergies is largely unknown and it is difficult to predict who will develop allergies to particular substances.

You are more likely to develop allergies if you:

  • Have a family history of asthma or allergies
  • Are a child
  • Have asthma or other allergies

Allergies Diagnosis

If you think you have an allergy, your health care provider can assist with making an accurate diagnosis by performing a physical exam and asking you questions, such as when the allergy occurs and what symptoms you experience.

Allergy testing can determine whether the symptoms are an actual allergy or are caused by other problems. For example, eating contaminated food may cause symptoms similar to food allergies. Some medications can produce itching and rashes, and a runny nose or cough may actually be due to an infection.

Skin testing is the most common method of allergy testing. Skin testing involves placing a small amount of the suspected allergen on the skin, and then closely watching for signs of a reaction, which include swelling and redness. Blood tests can also be done to measure levels of allergy-related substances in the body. You may also be asked to avoid exposure to suspected allergens to see if you get better, or to use suspected items to see if you feel worse.

Living With Allergies

Most allergies can be managed by avoiding exposure to allergens or taking medications to manage symptoms of an allergic reaction.

Some allergies are manageable with home remedies. For example, sinus congestion and symptoms of an allergy to pollen can be treated with nasal irrigation. Allergies to dust or pet dander can be managed with frequent washing of bedding and stuffed animals, maintaining low humidity in your home, regularly vacuuming carpet, or replacing carpet with hard-surface floors. Symptoms of mold allergies can be managed by reducing moisture in your home by using ventilation fans and dehumidifiers in rooms that remain damp, such as the kitchen and bathroom.

Having an allergy increases your risk of certain other medical problems, including:

  • Anaphylaxis. If you have severe allergies, you are at increased risk of this type of reaction. Anaphylaxis is most commonly associated with allergies to food, drugs, and insect venom.
  • Asthma.If you have an allergy, you are more likely to have asthma.
  • Atopic dermatitis (eczema), sinusitis, and infections of the ears or lungs. Your risk of getting these conditions is higher if you have an allergy to pollen, pet dander, or mold.
  • Fungal infections of your sinuses or your lungs. You are at increased risk of allergic fungal infections if you have an allergy to mold.

Allergies Treatments

Allergy treatment begins with avoiding the allergen that triggers your symptoms.

Medications can help relieve the symptoms related to allergies. Common antihistamines used to treat allergy symptoms include:

Antihistamines are often included as a component of combination cough and cold products. Review the labels of all medications carefully so you do not take more than 1 antihistamine at a time.

Immunotherapy (as allergy shots or sublingual tablets) may be necessary for severe allergies. This type of treatment involves long-term exposure to purified extracts of allergens to gradually increase the body’s tolerance to the substance and reduce the body’s development of a reaction.

Epinephrine (EpiPen, Auvi-Q, others) is recommended for severe allergic reactions. It should be injected as soon as the symptoms of a life-threatening reaction appear and can reduce the symptoms until emergency help arrives. If you have been diagnosed with a serious, potentially life-threatening allergy, you will likely carry epinephrine with you at all times.

Allergies Prognosis