ALLERGY
 
http://www.mayoclinic.com/health/allergies/DS01118/DSECTION=symptoms 
 

Allergies occur when your immune system reacts to a foreign substance such as pollen, bee venom or pet dander.

The immune system produces proteins known as IgE antibodies. These antibodies protect you from unwanted invaders that could make you sick or cause an infection. When you have allergies, your immune system makes antibodies that identify your particular allergen as something harmful, even though it isn't. This triggers the release of histamines and other substances that cause allergy symptoms.

Allergies can cause symptoms that involve 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 allergies can't be cured, a number of treatments can help relieve your allergy symptoms. 
 

Symptoms

Allergy symptoms depend on your particular allergy, and can involve the airways, sinuses and nasal passages, skin and digestive system. In most cases, an allergic reaction is a nuisance that causes irritating but minor symptoms. Severe allergic reactions can be more dangerous because they're likely to involve several of the body's organ systems. In some severe cases, allergies can trigger a life-threatening reaction in your body known as anaphylaxis.

Hay fever, also called allergic rhinitis, may cause:

  • Congestion
  • Itchy, runny nose
  • Itchy, watery or swollen eyes (conjunctivitis)

Atopic dermatitis, an allergic skin reaction also called eczema, may cause:

  • Itchy skin
  • Red skin
  • Flaking or peeling skin

A food allergy may cause:

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

An insect sting allergy may cause:

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

A drug allergy may cause:

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

Anaphylaxis 
Some types of allergies, including allergies to foods and insect stings, have the potential to trigger a severe reaction known as anaphylaxis. A life-threatening medical emergency, this reaction involves several of the body's organ systems and can cause you to go into shock. Signs and symptoms of anaphylaxis include:

  • Loss of consciousness
  • Lightheadedness
  • Severe shortness of breath
  • A rapid, weak pulse
  • Skin rash
  • Nausea and vomiting
  • Swelling airways, which can block breathing

When to see a doctor 
You may want to see a doctor if you have symptoms you think may be caused by an allergy, especially if you notice something in your environment that seems to trigger your allergies. 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 (such as EpiPen, EpiPen Jr or Twinject), give yourself a shot right away. Even if symptoms improve after an emergency epinephrine injection, a visit to the emergency department is still necessary 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.

 


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