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Am I Having an Allergic Reaction?

Recognizing and Treating Allergic Reactions


Updated May 28, 2014

Close-up of a young man wearing an oxygen mask
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If you've never had an allergic reaction before, it may be difficult to determine whether unusual symptoms after eating are due to an allergy, food poisoning, or something else entirely. Here are some "red flag" symptoms that can give you a good indication you're dealing with an allergy, plus what you can do immediately to treat an allergic reaction.

Watch the Timing

In general, symptoms of an allergic reaction show up within minutes of being exposed to the allergen. Some allergic reactions can occur after several hours. In rare cases, reactions develop after 24 hours. You should strongly suspect an allergy if symptoms begin almost immediately after eating, taking medication, or being stung by an insect.

Red Flag Symptoms

Severe allergic reactions generally cause swelling throughout the body. This can result in angioedema (swelling of the face, throat, genital and possibly bowels and arms/legs), hives (itchy welts that resemble insect bites and may appear in small groups or over large areas of the skin), or anaphylaxis (a severe, multi-system reaction that can cause difficulty breathing, changes in heart rate and blood pressure, and loss of consciousness). Allergic reactions can also cause swelling of the tongue and the throat, and allergies can trigger severe asthma attacks. If you have any of these symptoms, proceed to "Treating an Allergy" below.

Less Clear-Cut

Allergies can sometimes cause gastrointestinal symptoms like vomiting and diarrhea, but if these occur in isolation after eating a food you've never had problems with before, they're more likely to be food poisoning. If you're taking a medication, you may experience a wide variety of side effects -- from itchy skin to joint pain and more, depending on the medication. Drug Finder can help you determine which symptoms are common for your medication and which mean you should call your doctor or pharmacist. Allergies can sometimes cause tingling or itching in the mouth. Rhinitis (runny nose) after eating may indicate allergies, but is more often gustatory rhinitis, a form of non-allergic rhinitis.

Treating an Allergy

Anaphylaxis is a medical emergency. If you or a companion experience breathing difficulties, difficulty swallowing, fainting, loss of consciousness, or dramatic changes in heart rate after exposure to a potential allergen, call 911 (or your local emergency number) immediately and give epinephrine, if previously prescribed. An antihistamine like Benadryl may help ease symptoms while you wait for medical attention. If you have rescue medication prescribed for asthma, use it if allergy symptoms are accompanied by breathing difficulties, wheezing, or other asthma symptoms. After emergency treatment, follow up with your general practitioner or an allergist to determine what caused your reaction and how to prevent and treat reactions in the future.

Some allergic reactions are mild and can be treated at home with antihistamines. This includes hives over a small area of the body that aren't accompanied by other allergy symptoms, or an uncomplicated itchy mouth after eating. An itchy mouth warrants an appointment with your doctor, as it may indicate oral allergy syndrome. Likewise, if hives don't respond to a dose or two of antihistamine, cause considerable pain and itchiness, or appear every time you eat a certain food or take a particular medication, they indicate a call to your doctor. Your doctor may be able to prescribe topical medication to ease the itching and may want to test you for allergies.

Vomiting and diarrhea are less likely to be food allergy symptoms, but if they persist for more than 24 hours, or if fluid loss leads to symptoms of dehydration, call your doctor. You may need an anti-vomiting medication or, in severe cases, IV fluid replacement.


"Allergic Reactions." Medline Plus (NIH/NLM). Internet Resource. 15 June 2009.

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