Allergies

Allergies occur when the immune system reacts to substances that are usually harmless. These substances are called allergens and can include pollen, pet dander, insect venom, certain foods and some medicines. In people with allergies, the immune system mistakenly identifies these substances as dangerous.

The immune system produces antibodies to protect the body from harmful invaders such as bacteria and viruses. With allergies, the immune system makes antibodies that target a specific allergen even though it is not truly harmful. When the body comes into contact with that allergen, the immune response can cause inflammation in the skin, sinuses, airways or digestive system.

Allergic reactions vary widely. Some people experience mild symptoms such as sneezing or itching, while others may develop severe and life-threatening reactions known as anaphylaxis. Although most allergies cannot be cured, effective treatments are available to help control symptoms and reduce the risk of serious reactions.

Symptoms

Allergy symptoms depend on the type of allergen involved and which part of the body is affected. Reactions may involve the airways, sinuses, skin or digestive system. Symptoms can range from mild to severe.

Hay fever, also known as allergic rhinitis, may cause:

• Sneezing

• Itching of the nose, eyes, skin or roof of the mouth

• Runny or stuffy nose

• Tiredness or fatigue

• Watery, red or swollen eyes

Food allergies may cause:

• Tingling or itching in the mouth

• Swelling of the lips, tongue, face or throat

• Itchy welts called hives

• Stuffy nose, sneezing or itchy, watery eyes

• Stomach cramps, vomiting or diarrhea

• Anaphylaxis

Insect sting allergies may cause:

• Pain and large swelling at the sting site

• Itching or hives across the body

• Flushing or warmth of the skin

• Cough, chest tightness, wheezing or shortness of breath

• Anaphylaxis

Medicine allergies may cause:

• Hives

• Itchy skin or rash

• Swelling of the face

• Wheezing or difficulty breathing

• Vomiting or diarrhea

• Dizziness

• Anaphylaxis

Atopic dermatitis, also called eczema, may cause skin to:

• Itch

• Develop red or brown patches that may be less noticeable on darker skin

• Flake, peel or crack

Anaphylaxis is a severe allergic reaction that can be life-threatening. Symptoms may include:

• Loss of consciousness

• A sudden drop in blood pressure

• Severe shortness of breath or throat tightness

• Skin rash with hives

• Dizziness

• Rapid, weak pulse

• Nausea, vomiting or diarrhea

• A sense of impending doom

When to see a doctor

See a healthcare professional if you have allergy symptoms that do not improve with over-the-counter medicines or if symptoms appear after starting a new medication.

Seek emergency medical care immediately for a severe allergic reaction or symptoms of anaphylaxis. An injection of epinephrine is required to treat anaphylaxis. If you use an epinephrine auto-injector, go to the emergency room afterward to ensure symptoms do not return.

If you have a history of severe allergic reactions, schedule an appointment with a healthcare professional. Long-term management often involves allergy testing and working with a specialist called an allergist.

Causes

Allergies develop when the immune system mistakenly identifies a harmless substance as a threat. The immune system then produces antibodies that remain in the body. When exposure to the allergen happens again, these antibodies release chemicals that cause allergy symptoms.

Common allergy triggers include:

• Airborne allergens such as pollen, dust mites, mold and animal dander

• Foods such as peanuts, tree nuts, wheat, soy, fish, shellfish, eggs and milk

• Insect stings from bees or wasps

• Medicines, especially penicillin and related antibiotics

• Latex or other materials that come into contact with the skin

Risk factors

Several factors may increase the likelihood of developing allergies, including:

• A family history of allergies or asthma

• Childhood, as allergies are more common in children

• Having asthma or another allergic condition such as eczema

Complications

Allergies can increase the risk of other health conditions, including:

• Anaphylaxis, a severe and potentially life-threatening reaction

• Asthma, particularly allergy-induced asthma

• Infections of the sinuses, ears or lungs, especially in people with hay fever or asthma

Prevention

Preventing allergies focuses on avoiding known triggers and reducing exposure. Helpful strategies include:

• Staying away from substances that trigger your symptoms, even when taking allergy medicines

• Keeping windows closed and staying indoors when pollen counts are high

• Reducing dust mites by washing bedding regularly and using protective covers

• Keeping a diary of symptoms, activities and foods to help identify triggers

• Wearing a medical alert bracelet if you have a history of severe allergic reactions

Taking these steps, along with guidance from a healthcare professional, can help reduce allergy symptoms and lower the risk of serious reactions.