Allergies occur when your immune system reacts to a foreign substance â such as pollen, bee venom or pet dander â or a food that doesn't cause a reaction in most people.
Your immune system produces substances known as antibodies. When you have allergies, your immune system makes antibodies that identify a particular allergen as harmful, even though it isn't. When you come into contact with the allergen, your immune system's reaction can inflame your skin, sinuses, airways or digestive system.
The severity of allergies varies from person to person and can range from minor irritation to anaphylaxis â a potentially life-threatening emergency. While most allergies can't be cured, treatments can help relieve your allergy symptoms.
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:
- 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
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
A drug allergy can cause:
- Itchy skin
- Facial swelling
Atopic dermatitis, an allergic skin condition also called eczema, can cause skin to:
- Flake or peel
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
- A rapid, weak pulse
- Nausea and vomiting
When to see a doctor
You might see a doctor if you have symptoms you think are caused by an allergy, and over-the-counter allergy medications don't provide enough relief. 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 (Auvi-Q, 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.
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
To evaluate whether you have an allergy, your doctor will likely:
- Ask detailed questions about signs and symptoms
- Perform a physical exam
- Have you keep a detailed diary of symptoms and possible triggers
If you have a food allergy, your doctor will likely:
- Ask you to keep a detailed diary of the foods you eat
- Ask if you've stopped eating the suspected food during the allergy evaluation
Your doctor might also recommend one or both of the following tests. However, be aware that these allergy tests can be falsely positive or falsely negative.
- Skin test. A doctor or nurse will prick your skin and expose you to small amounts of the proteins found in potential allergens. If you're allergic, you'll likely develop a raised bump (hive) at the test location on your skin.
- Blood test. Specific IgE (sIgE) blood testing, commonly called radioallergosorbent test (RAST) or ImmunoCAP testing, measures the amount of allergy-causing antibodies in your bloodstream, known as immunoglobulin E (IgE) antibodies. A blood sample is sent to a medical laboratory, where it can be tested for evidence of sensitivity to possible allergens.
If your doctor suspects your problems are caused by something other than an allergy, other tests might help identify â or rule out â other medical problems.
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 â 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.
Preventing allergic reactions depends on the type of allergy you have. General measures include the following:
- Avoid known triggers. Even if you're treating your allergy symptoms, try to avoid triggers. If, for instance, you're allergic to pollen, stay inside with windows and doors closed when pollen is high. If you're allergic to dust mites, dust and vacuum and wash bedding often.
- Keep a diary. When trying to identify what causes or worsens your allergic symptoms, track your activities and what you eat, when symptoms occur and what seems to help. This may help you and your doctor identify triggers.
- Wear a medical alert bracelet. If you've had a severe allergic reaction, a medical alert bracelet (or necklace) lets others know that you have a serious allergy in case you have a reaction and you're unable to communicate.
Clinical practice guidelines suggest that some people with allergic rhinitis may benefit from acupuncture.
Lifestyle and home remedies
Some allergy symptoms improve with home treatment.
- Sinus congestion and hay fever symptoms. These often improve with saline nasal irrigation â rinsing out the sinuses with a salt and water solution. You can use a neti pot or a specially designed squeeze bottle to flush out thickened mucus and irritants from your nose. However, improper use of a neti pot or other device can lead to infection.
- Household airborne allergy symptoms. Reduce your exposure to dust mites or pet dander by frequently washing bedding and stuffed toys in hot water, maintaining low humidity, regularly using a vacuum with a fine filter such as a high-efficiency particulate air (HEPA) filter and replacing carpeting with hard flooring.
- Mold allergy symptoms. Reduce moisture in damp areas, such as your bath and kitchen, by using ventilation fans and dehumidifiers. Fix leaks inside and outside your home.
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
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