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

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

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

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.