Overview

Allergies occur when your immune system reacts to a foreign substance — such as pollen, bee venom or pet dander — or a food that doesn't cause a reaction in most people.

Your immune system produces substances known as antibodies. When you have allergies, your immune system makes antibodies that identify a particular allergen as harmful, even though it isn't. When you come into contact with the allergen, your immune system's reaction can inflame your skin, sinuses, airways or digestive system.

The severity of allergies varies from person to person and can range from minor irritation to anaphylaxis — a potentially life-threatening emergency. While most allergies can't be cured, treatments can help relieve your allergy symptoms.

Symptoms

Allergy symptoms, which depend on the substance involved, can affect your airways, sinuses and nasal passages, skin, and digestive system. Allergic reactions can range from mild to severe. In some severe cases, allergies can trigger a life-threatening reaction known as anaphylaxis.

Hay fever, also called allergic rhinitis, can cause:

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

A food allergy can cause:

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

An insect sting allergy can cause:

  • A large area of swelling (edema) at the sting site
  • Itching or hives all over the body
  • Cough, chest tightness, wheezing or shortness of breath
  • Anaphylaxis

A drug allergy can cause:

  • Hives
  • Itchy skin
  • Rash
  • Facial swelling
  • Wheezing
  • Anaphylaxis

Atopic dermatitis, an allergic skin condition also called eczema, can cause skin to:

  • Itch
  • Redden
  • Flake or peel

Anaphylaxis

Some types of allergies, including allergies to foods and insect stings, can trigger a severe reaction known as anaphylaxis. A life-threatening medical emergency, anaphylaxis can cause you to go into shock. Signs and symptoms of anaphylaxis include:

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

When to see a doctor

You might see a doctor if you have symptoms you think are caused by an allergy, and over-the-counter allergy medications don't provide enough relief. If you have symptoms after starting a new medication, call the doctor who prescribed it right away.

For a severe allergic reaction (anaphylaxis), call 911 or your local emergency number or seek emergency medical help. If you carry an epinephrine auto-injector (Auvi-Q, EpiPen, others), give yourself a shot right away.

Even if your symptoms improve after an epinephrine injection, you should go to the emergency department to make sure symptoms don't return when the effects of the injection wear off.

If you've had a severe allergy attack or any signs and symptoms of anaphylaxis in the past, make an appointment to see your doctor. Evaluation, diagnosis and long-term management of anaphylaxis are complicated, so you'll probably need to see a doctor who specializes in allergies and immunology.

Causes

An allergy starts when your immune system mistakes a normally harmless substance for a dangerous invader. The immune system then produces antibodies that remain on the alert for that particular allergen. When you're exposed to the allergen again, these antibodies can release a number of immune system chemicals, such as histamine, that cause allergy symptoms.

Common allergy triggers include:

  • Airborne allergens, such as pollen, animal dander, dust mites and mold
  • Certain foods, particularly peanuts, tree nuts, wheat, soy, fish, shellfish, eggs and milk
  • Insect stings, such as from a bee or wasp
  • Medications, particularly penicillin or penicillin-based antibiotics
  • Latex or other substances you touch, which can cause allergic skin reactions

Risk factors

You might be more likely to develop an allergy if you:

  • Have a family history of asthma or allergies, such as hay fever, hives or eczema
  • Are a child
  • Have asthma or another allergic condition

Complications

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

  • Anaphylaxis. If you have severe allergies, you're at increased risk of this serious allergy-induced reaction. Foods, medications and insect stings are the most common triggers of anaphylaxis.
  • Asthma. If you have an allergy, you're more likely to have asthma — an immune system reaction that affects the airways and breathing. In many cases, asthma is triggered by exposure to an allergen in the environment (allergy-induced asthma).
  • Sinusitis and infections of the ears or lungs. Your risk of getting these conditions is higher if you have hay fever or asthma.

Prevention

Preventing allergic reactions depends on the type of allergy you have. General measures include the following:

  • Avoid known triggers. Even if you're treating your allergy symptoms, try to avoid triggers. If, for instance, you're allergic to pollen, stay inside with windows and doors closed when pollen is high. If you're allergic to dust mites, dust and vacuum and wash bedding often.
  • Keep a diary. When trying to identify what causes or worsens your allergic symptoms, track your activities and what you eat, when symptoms occur and what seems to help. This may help you and your doctor identify triggers.
  • Wear a medical alert bracelet. If you've had a severe allergic reaction, a medical alert bracelet (or necklace) lets others know that you have a serious allergy in case you have a reaction and you're unable to communicate.
Aug. 07, 2017
References
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