An allergic reaction happens when your immune system defends against substances that otherwise wouldn’t pose a threat to your body. Common allergens include pollen, mold, and certain foods.
Your immune system is responsible for defending the body against bacteria and viruses. In some cases, your immune system will defend against substances that typically don’t pose a threat to the human body. Some of these substances are known as allergens, and when your body reacts to them, it causes an allergic reaction.
You can have an allergic reaction after inhaling, eating, or touching an allergen. Doctors can also use allergens to diagnose allergies and can even inject them into your body as a form of treatment.
The American College of Allergy, Asthma & Immunology (ACAAI) reports that over 50 million people in the United States have some type of allergy.
Doctors don’t know why some people experience allergies. Allergies appear to run in families, which means they can be inherited. If you have a close family member who has allergies, you’re at greater risk for developing them.
The reasons why allergies develop are unclear, but some substances are known to commonly cause an allergic reaction. People who have allergies are typically allergic to one or more of the following:
- pet dander, such as the kind from a cat or dog
- bee stings or bites from other insects
- certain foods, including nuts and shellfish
- certain medications, such as penicillin and aspirin
- certain plants
- pollen
- mold
- dust mites
The symptoms of an allergic reaction can vary from mild to severe. If you become exposed to an allergen for the first time, your symptoms may be mild. These symptoms may get worse if you repeatedly come into contact with the allergen.
Mild reaction
Symptoms of a mild allergic reaction can include:
- hives, or itchy red spots on the skin
- rash
- itching
- allergic rhinitis, which may lead to symptoms such as nasal congestion or sneezing
- scratchy throat
- watery or itchy eyes
Severe reaction
Severe allergic reactions (usually to foods, insect stings, and medications) can cause the following symptoms:
- abdominal cramping or pain
- diarrhea
- nausea or vomiting
- pain or tightness in the chest
- difficulty swallowing
- difficulty breathing
- wheezing
- fear or anxiety
- heart palpitations
- flushing of the face
- swelling of the face, eyes, or tongue
- dizziness or vertigo
- weakness
- unconsciousness
A severe and sudden allergic reaction known as anaphylaxis can develop just seconds after exposure to an allergen. This type of reaction results in life threatening symptoms, including:
- swelling of the airway
- an inability to breathe
- a sudden and severe drop in blood pressure
If you experience anaphylaxis, seek immediate emergency help. Without treatment, anaphylaxis can result in death.
A primary care physician or an allergist can diagnose allergic reactions.
If you experience symptoms of an allergic reaction, the doctor will perform an exam and ask you about your health history. If your allergic reactions are severe, they may ask you to keep a journal that details your symptoms and the substances that appear to cause them.
The doctor may want to order tests to determine what’s causing your allergy. The most commonly ordered types of allergy tests are:
- skin tests
- challenge (elimination-type) tests
- blood tests
Skin test
A skin test involves applying a small amount of a suspected allergen to the skin and watching for a reaction. The substance may be:
- taped to the skin (patch test)
- applied via a small prick to the skin (skin prick test)
- injected just under the skin (intradermal test)
A skin test is most valuable for diagnosing:
- food allergies, such as allergies to shellfish or peanuts
- mold, pollen, and animal dander allergies
- penicillin allergies
- allergies to venom, such as the kind secreted by bees or yellow jackets
- allergic contact dermatitis, which is a rash you get after touching a substance
Challenge (elimination-type) test
Challenge testing is useful in diagnosing food allergies. It involves removing a food from your diet for several weeks and carefully watching for symptoms when you eat the food again.
Blood test
A blood test allows the doctor to check your blood for antibodies against a possible allergen. An antibody is a protein your body produces to fight harmful substances.
Blood tests are an option when skin testing isn’t helpful or possible.
If you experience an allergic reaction and you don’t know what’s causing it, you may need to see a doctor to determine which substances you’re allergic to. If you have a known allergy and experience symptoms, you may not need to seek medical care if your symptoms are mild.
In most cases, over-the-counter antihistamines, such as diphenhydramine (Benadryl), can be effective in controlling mild allergic reactions.
Treatment for anaphylaxis
If you or someone you know experiences a severe allergic reaction, you should seek emergency medical attention. Check to see if the person is breathing, call 911 or your local emergency services, and provide CPR if needed.
People with known allergies often have emergency medications with them, such as an epinephrine auto-injector (EpiPen, Adrenaclick, Auvi-Q). Epinephrine is deemed a “rescue drug†because it opens the airways and raises blood pressure.
The person may need your help to administer the medication. If the person is unconscious, follow these steps to help prevent shock:
- lay them on their side
- elevate their legs
- cover them with a blanket
Once you identify what’s causing your allergic reaction, you can take the following steps:
- avoid exposure to the allergen
- seek medical care if you’re exposed to the allergen
- carry medications to help treat anaphylaxis
You may not be able to avoid an allergic reaction completely, but these steps can help you prevent future allergic reactions.
If you have a known allergy, preventing an allergic reaction will improve your outlook. You can do this by avoiding your allergens whenever possible.
Your outlook will also depend on the severity of your allergy.
If you have a mild allergic reaction and seek treatment, you’ll have a good chance of recovery. However, symptoms may return if you come into contact with the allergen again.
If you have a severe allergic reaction, your outlook will depend on receiving quick emergency care, since anaphylaxis can result in death. If you have severe allergies, always carry an epinephrine auto-injector and inject yourself if symptoms occur.
Prompt medical care is also necessary to improve your outcome.