Man with possible allergic reaction petting cat

What are the signs and symptoms of an allergic reaction?

Medically reviewed on August 1, 2022 by Jillian Foglesong Stabile, MD, FAAFP. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.

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When something happens to your body that you don’t expect or understand, it’s important to have the necessary tools and knowledge. Allergic reactions can fall into that category. Sometimes, you don’t even know that you’re allergic to something until you have an unexpected reaction. So how do I know if I’m having an allergic reaction?

Luckily, there are signs and symptoms that you can look out for to know when you might be allergic. With this information at hand, you can be better prepared if you or someone close to you has an allergic reaction.

To start, you’ll want to learn how and why your body might respond to an allergen. We’ll also give you some tips on common allergy causes and ways to prevent reactions before they occur.

5 symptoms that can indicate an allergic reaction

First, let’s answer one vital question that might be on your mind: how do I know if I’m having an allergic reaction?

It can be difficult to tell if you’re having an allergic reaction in some cases because there are different types of allergic reactions, each coming with its own set of symptoms.

Five common ways in which your body tells you that you’re allergic to something can include: [1]

  1. Anaphylaxis
  2. Eye irritation
  3. Sinus and nasal reactions
  4. Skin reactions
  5. Digestive system responses

Let’s look at each of these in more detail so that you better understand their unique symptoms.


The most serious of allergic reactions can result in Anaphylaxis. [2] Anaphylactic shock is a life-threatening, severe allergic reaction to an allergy trigger. When your body faces an allergen, it responds by producing antibodies to counter that allergen. Your body also releases histamine. This chemical is also responsible for some less serious reactions like watery eyes or itchy skin.

However, in some cases, your body goes into overdrive and produces a huge influx of chemicals in response. These chemicals can cause you to go into shock. Your blood pressure can drop suddenly, and your body struggles to get enough oxygen. You might experience the following symptoms as a result:

  • Difficulty breathing
  • A sudden skin rash
  • Nausea and vomiting
  • Weak or rapid pulse
  • Tightening in the throat
  • Dizziness or fainting

Anaphylaxis can occur within minutes of coming into contact with an allergen. However, it may take longer, and a second severe reaction can occur as many as twelve hours after the initial response. People who suffer from this kind of severe allergic reaction should always carry an epinephrine auto injector.

If you experience any of the signs of anaphylaxis, you should seek emergency care right away.

Eye reactions

Fortunately, not all allergic reactions are life-threatening. Some cause reactions or irritation in other parts of the body—and eye allergies are one such type.

Your eyes are sensitive organs and can respond to allergens in several ways. You may have come into contact with an allergen that affects your eyes if you experience: [3]

  • Itchy eyes
  • Redness
  • Tears or watery eyes
  • General pain or irritation in the eyes
  • Swelling of the eyelids

Eye allergies typically occur when an irritant enters your eyes. Some common allergens that can irritate eyes include pollen, mold, dust, and pet dander. Pollutants and chemicals can also cause a mild allergic reaction in your eyes.

Sinus and nasal reactions

You can also experience an allergic reaction in your sinuses or nose. Nasal and sinus allergic reactions can have similar symptoms, including: [1]

  • Increase in mucus production and drainage
  • Coughing and sneezing
  • Congestion
  • Runny nose
  • Itchy eyes
  • Headaches
  • Irritated throat
  • Allergic rhinitis

These allergic reactions typically result from airborne irritants.

Skin reactions

Your skin can also respond to allergens and exhibit symptoms of an allergic reaction. Chemicals, dust mites, certain metals, and plants can sometimes cause a mild reaction on the skin. There are four common skin allergy symptoms, including: [4]

  • Eczema – Eczema typically appears as a dry, itchy, inflamed rash. Some types of eczema can be triggered by a food allergy, so knowing the cause is an essential part of treating this symptom.
  • Contact dermatitis – Contact dermatitis appears when your skin comes into direct contact with an allergen. For example, if you’re allergic to sunflower oil and you accidentally use a lotion containing this ingredient, you will likely get a red, bumpy, itchy rash on your skin. Plants like poison ivy and poison oak can also cause a similar allergic response.
  • Hives – Hives occur when your body releases histamine as a response to an allergen. Hives happen when your blood vessels leak into the skin. This can make the skin swell into painful, red welts. Hives can be a response to many different types of allergens, including food, medications, or even insect bites.
  • Angioedema – Angioedema is also caused by swelling in the skin tissue, although it typically occurs in softer areas. The mouth, eyelids, and genitals are specifically prone to angioedema swelling. This reaction is often caused by allergens in food or medications.

Digestive system reactions

Finally, you can experience symptoms of an allergic reaction in your digestive tract. Typically, digestive systems symptoms of an allergic reaction are caused by ingesting food you have an allergy to.

Some of the common symptoms you might experience when an allergen comes into contact with your digestive tract include: [5]

  • Nausea
  • Vomiting
  • Stomach cramping
  • Gas and bloating
  • Diarrhea
  • Heartburn

If you’re experiencing digestive issues, it’s important not to ignore them. In some cases, just removing the allergen from your diet can be immensely helpful in relieving your symptoms. Because food allergies can worsen over time, abstaining from your triggers can also help you to avoid more severe symptoms in the future.

What are some common allergy triggers?

There are many things people can be allergic to. We all have different immune systems with differing levels of sensitivity.

That being said, there are some fairly common allergy triggers, including: [6]

  • Foods – Certain foods are known to cause allergies. The most common are peanuts, shellfish, tree nuts, milk, eggs, soy, wheat, fish, and sesame. Some people may not be allergic to specific foods as children but then develop an allergy as they get older. Certain food allergies, for example, to nuts and tree nuts can sometimes cause an anaphylactic reaction. Understanding what causes a peanut allergy can be critical to avoiding a severe allergic reaction.
  • Insect bites or stings – Insect bites and stings can also cause moderate to severe allergic reactions. Wasps, bees, and ants are all common insects that can cause problems for allergy sufferers. In extreme cases, insect bites and stings can cause anaphylaxis.
  • Airborne allergens – There are many airborne causes of allergic reactions. Some common ones include dust, pollen, mold, and pet dander. Pollen allergies or hay fever are typically more prominent in the spring and fall.
  • Medications – Some medications can also trigger allergic reactions. Penicillin is one common medicine that can cause an immune response in some people. Other people may be allergic to certain antibiotics, aspirin, ibuprofen, and chemotherapy drugs. An allergic reaction to medication can range from a mild reaction to severe anaphylactic shock.

How are allergies diagnosed?

Finding out what you’re allergic to can be tricky because some allergy symptoms can resemble those of other illnesses. The good news is that there are diagnostic tools and methods you and healthcare providers can use to determine if you have an allergy.

These tools might include: [7]

  • A discussion of your medical history
  • Physical exams
  • Skin-prick tests
  • Blood tests
  • Intradermal skin tests
  • Patch tests
  • Supervised exposure to allergens

What type of testing your healthcare provider will use to determine if you have an allergy depends on the type of allergy being tested. Patch tests can help to identify if someone has a skin allergy. In contrast, skin-prick tests and blood tests might be used to screen for food allergies. Supervised exposure tests might determine if you are allergic to a specific medication.

How do you treat an allergic reaction?

The best method for treating an allergic reaction depends on the type and severity of the reaction. If you have an anaphylactic response, you will likely need emergency medical treatment as this is a life-threatening situation. Once you’ve been diagnosed with a severe allergy, your healthcare professional will also likely prescribe you an EpiPen so that you can administer medication yourself immediately upon experiencing an allergic reaction.

In less severe cases, allergies can be treated with: [8]

  • Antihistamine medication
  • Decongestants
  • Steroid medications
  • Lotions and creams for skin reactions

Once you know what you are allergic to and how your body responds to it, your healthcare provider can prescribe the best option for your specific allergies, symptoms, and severity.

Can you prevent allergic reactions?

The best way to prevent allergic reactions is to avoid contact with the allergens that cause your reactions.

Avoiding your allergens is often easier said than done. In cases where you know you’re allergic to a specific food or medication, you can simply not eat or take the substance.

However, when airborne elements cause your allergies, avoiding the allergens that irritate you can be much more challenging. In these cases, medications like antihistamines can help to reduce your allergy symptoms, if not eliminate them.

Allergies can crop up at any time during your life. Something you weren’t allergic to as a child might still cause a reaction when you’re older. No matter when your reaction happens, knowing the signs and symptoms is the first step toward identifying a problem and preventing it from happening again.

As we mentioned above, some of the most common allergies involve food. If you've experienced any mild allergic reaction symptoms after eating a specific type of food, it would be wise to test for a food allergy.

The Everlywell Food Allergy Test is an excellent place to start. Our easy-to-use, convenient, at-home test can screen for nine of the most common food allergens. If your results show that you might have an allergy, we’ll guide you through the next steps. Additionally, you can test for reactivity to environmental allergens with the at-home Indoor & Outdoor Allergy Test.

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  1. Allergies. Asthma and Allergy Foundation of America. URL. Accessed August 1, 2022.
  2. Anaphylaxis. American College of Allergy, Asthma, & Immunology. URL. Accessed August 1, 2022.
  3. Allergy. PubMed. URL. Accessed August 1, 2022.
  4. Skin Allergies. American Academy of Allergy, Asthma, & Immunology. URL. Accessed August 1, 2022.
  5. Food Allergies. FDA. URL. Accessed August 1, 2022.
  6. Allergy Facts and Figures. Asthma and Allergy Foundation of America. URL. Accessed August 1, 2022.
  7. Allergy Diagnosis. Asthma and Allergy Foundation of America. URL. Accessed August 1, 2022.
  8. Allergies. NHS. URL. Accessed August 1, 2022.
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