Symptoms and causes

Symptoms

Allergy symptoms depend on the substance involved and can affect the 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, may cause:

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

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 the body
  • Cough, chest tightness, wheezing or shortness of breath
  • Anaphylaxis

A drug allergy may cause:

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

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

  • Itch
  • Redden
  • Flake or peel

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, 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 may be caused by an allergy, especially if you notice something that seems to trigger your symptoms. 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, 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 bee stings or wasp stings
  • Medications, particularly penicillin or penicillin-based antibiotics
  • Latex or other substances you touch, which can cause allergic skin reactions

Risk factors

You may be at increased risk of developing an allergy if you:

  • Have a family history of asthma or allergies. You're at increased risk of allergies if you have family members with asthma or allergies such as hay fever, hives or eczema.
  • Are a child. Children are more likely to develop an allergy than are adults. Children sometimes outgrow allergic conditions as they get older.
  • Have asthma or another allergic condition. Having asthma increases your risk of developing an allergy, and vice versa. Also, having one type of allergic condition makes you more likely to be allergic to something else.

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.
  • Fungal complications of your sinuses or your lungs. You're at increased risk of getting these conditions, known as allergic fungal sinusitis and allergic bronchopulmonary aspergillosis, if you have an allergy.