How to Tell If You Are Having an Allergic Reaction (and What to Do)
Medically reviewed by Daniel More, MDMedically reviewed by Daniel More, MDDuring an allergic reaction, your immune system overreacts when exposed to an allergen. If your immune system has become overly sensitized, you might have an allergic reaction after you inhale, eat, or touch the allergen, even if it doesn't cause the same reaction in others around you.To diagnose allergies, a healthcare provider may try to identify the specific allergens that trigger your immune system, such as grass pollen, bee stings, or dust mites. Some people also choose to get immunotherapy, treatments specifically targeted to help reduce their immune overreaction to specific allergens.
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What Causes an Allergic Reaction?An allergic reaction happens when part of your immune system becomes abnormally programmed to overreact to a substance in the environment. It most commonly involves excess release of an antibody called immunoglobulin E (IgE).Certain substances can confuse the immune system and trigger allergic reactions much more commonly than others, such as:Certain drugs, such as penicillin and nonsteroidal anti-inflammatory drugs (NSAIDs)Dust mitesFoods, such as eggs, shellfish, or peanutsInsect stingsMoldPet danderPollenSome items you touch, such as latex, metals like nickel, or certain health and beauty products, might also trigger an allergic reaction. However, metal and cosmetic allergies are not usually due to IgE but rather to delayed-type hypersensitivity (DTH) that results in contact dermatitis. DTH is not usually a dangerous or life-threatening allergy the way an IgE-mediated reaction can be.What Does an Allergic Reaction Look Like?Symptoms of a Mild ReactionMild allergic reactions and symptoms can affect your skin, eyes, nose, or respiratory system and include the following:Allergic asthmaEczemaHives or other rashesRed, itchy, watery eyesRunny noseShortness of breathSneezingWheezingInhaled allergens (e.g., seasonal allergies from exposure to pollen) may produce chronic symptoms but are not as severe as acute (short-term) allergies from substances you're not usually exposed to (e.g., a peanut allergy).
Related: Allergy Symptoms
Symptoms of a Severe ReactionThe most severe allergic reaction is a rare but life-threatening response known as anaphylaxis. It usually occurs within minutes of exposure to an allergen, though it could take up to a couple of hours in some cases.Anaphylaxis usually affects at least two organ systems in the body. In addition to less severe symptoms, like itchy rash, which is often present, it can cause severe symptoms such as:Abdominal pain, vomiting, and/or diarrheaChest painCoughing and wheezingSignificant difficulty breathingSwelling of the tongue and/or throatAnaphylaxis can also cause hypotension (low blood pressure), characterized by flushed skin, confusion, loss of consciousness, or (very rarely) death. The most common triggers of anaphylaxis are foods (such as peanuts), medications, and insect stings.
When to Seek Emergency CareCall 911 or your local emergency number if you experience anaphylaxis symptoms such as difficulty breathing, throat swelling, or signs of low blood pressure. Severe allergic reactions can be life-threatening. When in doubt, seek immediate treatment.
How Is an Allergic Reaction Diagnosed?Skin TestThe most common allergy skin test is the skin prick test. During this test, a healthcare provider pricks your skin with a small amount of an allergen. If the area becomes red within 15 minutes, you might be allergic to the substance.These tests are not perfect, and some people tolerate certain substances fine, even if they get a reaction via a skin test. Skin testing doesn’t measure allergy severity.Challenge (Elimination-Type) TestChallenge-type allergy tests are an option for allergens that can be completely eliminated, such as certain foods from your diet.Design your challenge with the help of a healthcare provider. During the challenge, you’ll remove one or more potential triggers from your diet for several weeks. Then, slowly reintroduce potential allergens one at a time. Experiencing a reaction is a clue you might be allergic to that substance.This approach may not be appropriate and safe for everyone (e.g., someone who has previously experienced anaphylaxis). Some people should only perform challenge testing under direct clinical supervision.Blood TestsHealthcare providers use a specific blood test called total IgE, which measures the immunoglobulin E antibodies in your blood. High IgE levels indicate an allergy, but the test doesn't provide information about the specific allergen. A similar blood test is the specific IgE test. It looks at the IgE antibodies you have to specific substances. However, these IgE tests can't indicate potential allergy severity.The basophil activation test (BAT) is a blood test that can also assess whether you might be allergic to certain substances. It is a more conservative measure than specific IgE tests.Scientists are also developing mast cell activation tests (MAT) that use mice mast cells incubated with patient serum, which are then exposed to the allergen. (This test is an alternative to the BAT, in which providers use the patient's basophils, which is a much more extensive—and expensive—process).What Can You Do for an Allergic Reaction at Home?There are a few options for treating mild allergic reactions at home, including:Over-the-counter (OTC) antihistamine medication, such as Benadryl (diphenhydramine) or Claritin (loratadine)OTC nasal sprays or eye drops to help soothe seasonal allergy symptomsOTC lotions for a rash, such as a corticosteroid cream or calamine lotionA cool bath with added baking soda to help reduce itchA cool compress (moistened washcloth) and loose clothes to avoid additional skin irritationIf you experience mild but persistent allergic symptoms, seek the advice of a healthcare provider.How Anaphylaxis Is TreatedCall 911 to get immediate guidance and emergency treatment for any signs of anaphylaxis, like severe throat swelling or difficulty breathing.If available, use an epinephrine auto-injector (EpiPen) to administer epinephrine to the symptomatic person's thigh as soon as possible. People at risk of serious allergic reactions may carry EpiPens with them. After administering the EpiPen, have them lie down with their legs elevated. If the affected person passes out, monitor their breathing and heart rate. If they stop breathing, you can give rescue breaths if you've been trained to do this. If they don't have a pulse, administer CPR (cardiopulmonary resuscitation). Even if you haven't been officially trained, you can give chest compressions (without rescue breaths).Emergency care providers will give epinephrine (if not previously given) and closely monitor the person to see what other treatments they may need, such as intravenous (IV) fluids, inhaled oxygen, or medications to open the airways or the lungs.Even if symptoms resolve after administering epinephrine, seeing an emergency healthcare provider is a good idea. They may need to monitor you for a while in case you have another anaphylactic response, which sometimes happens after the first one.
TakeawayDrugs like Benadryl may help reduce skin symptoms in someone with anaphylaxis. However, they are not effective in reducing potentially life-threatening symptoms of anaphylaxis and should never be used in place of initial epinephrine.
Can You Prevent an Allergic Reaction?If you have a known allergy to a specific substance, you can avoid the substance to prevent an allergic reaction. For example, someone allergic to peanuts can try to avoid peanut products. Even if you cannot completely avoid an allergen, you might be able to lower your exposure and decrease your symptoms. For example, thorough and regular household cleaning may decrease allergies to dust mites.Immunotherapy is an approach healthcare providers may recommend to reduce your risk of allergic reactions in the long term. After an allergist has identified the specific allergens to which you react, you get specifically designed allergy shots or dissolving tablets over months. Over time, you may reduce or eliminate your allergic response. What Is the Long-Term Outlook?Sometimes, you might be allergic to a substance, with either a mild or severe allergy, but eventually lose the allergy. However, other people might experience allergy symptoms from the triggering substance for the rest of their lives unless they receive immunotherapy to help eliminate them. Most people who experience anaphylaxis will fully recover without any long-term issues. However, roughly 1 in 400 cases of anaphylaxis are fatal. Anaphylaxis can also cause long-term problems in an extremely small minority of people, like permanent kidney or brain damage. People who are not treated have relatively higher risks of long-term complications compared to those who are. Certain medical conditions, like asthma, might also increase your risk, as might very young or old age.SummaryIn an allergic reaction, your body overreacts to a substance in the environment that you’ve inhaled, eaten, or touched. This response might be mild, like slightly itchy and red eyes, or cause a life-threatening reaction called anaphylaxis.Healthcare providers often diagnose allergic reactions based on your symptoms and medical history. However, skin tests, elimination tests, and blood tests are potential options to identify specific allergen triggers. Treatment ranges from over-the-counter medications to emergency intervention in a healthcare setting. Read the original article on Verywell Health.
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