Symptoms & Causes

Causes

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. 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.

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. 

Common allergens include:

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

Symptoms

The part of the body the allergen touches affects which symptoms you develop.

For example:

  • Allergens that you breathe in often cause a stuffy nose, itchy nose and throat, mucus, cough, wheezing.
  • Allergens that touch the eyes may cause itchy, watery, red, swollen eyes.
  • Eating something you are allergic to can cause nausea, vomiting, abdominal pain, cramping, diarrhea, or a severe, life-threatening reaction.
  • Allergens that touch the skin can cause a skin rash, hives, itching, blisters, or skin peeling.
  • Drug allergies usually involve the whole body and can lead to a variety of symptoms.

Symptoms of allergies include the following:

  • Runny nose and mucus production
  • Sneezing
  • Itchy nose, eyes, ears, and mouth
  • Stuffy nose
  • Red and watery eyes
  • Swelling around the eyes
  • Coughing
  • Wheezing
  • Chest tightness
  • Shortness of breath