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How Long Do Symptoms of a Food Allergy Reaction Last?

Medically reviewed by Shruti Wilson, M.D.
Updated on November 1, 2023

Many people with food allergies have an allergic reaction within a few minutes of eating a food allergen. Nearly all reactions happen within two hours after exposure to proteins in specific types of food like shellfish or tree nuts. However, in some rare cases, an allergic reaction to food takes hours to develop.

Whatever the timing, using medication as soon as you have symptoms can help you regain control faster. Although everyone’s experience is different, here’s how long it usually takes for food allergy symptoms to resolve.

Many Allergic Reactions Quickly Respond to Epinephrine

Allergic reactions to food are usually treated with epinephrine auto-injector shots, such as an Auvi-Q or EpiPen. These powerful medications are the quickest way to reverse an allergic reaction. Epinephrine enters the bloodstream and immediately starts reducing swelling, hives, low blood pressure, gastrointestinal (GI) symptoms, and breathing problems. You should see a difference within a few minutes.

Epinephrine shots are most effective when you use one shortly after exposure to a food trigger. Delaying treatment increases the risk of death from anaphylaxis (a severe allergic reaction). Always call 911 or seek emergency medical care after administering an epinephrine shot.

Biphasic Reactions Can Happen Hours After Exposure

Sometimes, even after epinephrine treatment, food allergies cause a biphasic reaction, or a second wave of symptoms. Although the first reaction subsides, the next round of symptoms may need additional treatment. This second reaction usually happens one to four hours after the first. Studies have found between 1 percent and 20 percent of people with food allergies may have a biphasic reaction, and there’s no way to predict who will be affected. This is why seeking emergency medical treatment is critical.

Timing Other Types of Treatment

You may be able to treat less severe food allergy symptoms with antihistamines or targeted medications called H1 or H2 receptor blockers. Unlike epinephrine, which (outside the hospital) is typically injected intramuscularly (into the muscles) or subcutaneously (under the skin), you take these treatments by mouth. Since they need to go through the digestive system first, it takes a little longer for oral medications to have an effect on food allergy symptoms. (Antihistamines are mainly intended to treat mild skin symptoms like itching or a few hives.)

Antihistamines like diphenhydramine (Benadryl) and cetirizine (Zyrtec) start working within about 15 minutes. Diphenhydramine takes between 15 and 60 minutes to have an effect, and cetirizine takes 15 to 30 minutes. Both of these medications are available without a prescription, but they are only meant for kids of a certain age. Be sure to check with your doctor to determine if over-the-counter treatments are suitable for your or your child’s food allergies.

When To Seek Emergency Care

Although oral medication can help with some milder allergy symptoms, it’s not a substitute for the lifesaving injections needed to treat anaphylaxis. Use epinephrine right away if you have the following symptoms:

  • Abdominal pain
  • Repetitive vomiting and diarrhea
  • Frequent coughing
  • Swelling
  • Throat tightness
  • Trouble breathing
  • Weak pulse
  • Hives
  • Dizziness or feeling faint

Your doctor or allergist can help you create an anaphylaxis emergency care plan so you’ll know exactly what to do if a severe allergic reaction occurs.

You may need to ride in an ambulance to the emergency room if you’re showing symptoms of anaphylaxis, especially difficulty breathing, dizziness, throat tightness, tongue swelling, or repetitive vomiting. Be sure to inform the dispatcher if you’ve already injected epinephrine or taken another allergy medication.

You should also follow up with your doctor when nausea and vomiting don’t improve after allergy treatment. In addition to food allergies, these GI symptoms may be caused by food intolerance, ulcers, or an infection (like the stomach flu).

How Long Will Symptoms Last Without Treatment?

There isn’t much data on how long food allergy symptoms take to resolve without treatment. There’s also a chance that symptoms won’t get better on their own. If you have a known food allergy, it’s crucial not to take a chance. Untreated symptoms can progress to a life-threatening anaphylactic reaction, and treating them promptly gives you the best chance of staying safe and out of the emergency room.

Factors such as how much of the food allergen you ate can affect how your body reacts. Allergy testing identifies specific food triggers so you know what to avoid and when to treat your symptoms. If your doctor determines that your allergy is severe enough to warrant an epinephrine auto-injector, you shouldn’t hesitate to use it during an emergency. The risks of using the auto-injector when it’s not needed are lower than the risks of not using it when in danger of anaphylaxis.

If it’s been a long time since your last allergic reaction, you may be wondering if you still need to take precautions. To see if you’ve outgrown a food allergy, make an appointment with an allergist. The allergist may order skin prick tests or blood tests, or they may supervise you during an oral food challenge that includes an observation period to watch for a reaction with emergency treatment nearby.

How To Avoid Continued Exposure

Unlike people with environmental allergies like hay fever, who may require ongoing treatment, people with food allergies can avoid their triggers and stay prepared for accidental exposures. After an allergic reaction to food, it can take hours to days before you feel better. It’s important to follow up with your health care provider if your symptoms aren’t improving or seem to be getting worse despite treatment.

Symptoms of an allergic reaction can range from tingling of the mouth to severe nausea, vomiting, and shortness of breath. Even if you have had reactions in the past, every reaction can differ and bring about new and unpredictable symptoms. To avoid future exposure to your food allergens, you’ll need to read food labels, find food products and brands that are allergen free, learn to prepare allergy-free meals, and navigate restaurant menus. If you need help, ask your doctor for a referral to a registered dietitian nutritionist who can teach you strategies to avoid your food allergens.

Treating Food Allergies To Prevent Future Reactions

Scientists are developing new immunotherapies intended to reduce the likelihood of severe food allergy reactions. Some of these therapies work based on the premise that regular, carefully controlled exposure to tiny amounts of an allergen over time can help your body’s immune system become less sensitive to it.

Another approach under development is the use of biologic drugs — human-made versions of immune system proteins — to target immunoglobulin E (IgE), a protein responsible for setting off allergic reactions. By binding with and neutralizing IgE, biologic drugs could help prevent the processes that lead to allergic reactions and life-threatening anaphylaxis.

If you’re curious about new strategies for treating food allergies, ask your allergist to let you know about new treatments as they become available.

Discussions on MyFoodAllergyTeam

Food allergies affect people differently. Although you can read textbook examples of the common symptoms and responses to treatment, you may also relate to other people’s real-life experiences.

One MyFoodAllergyTeam member shared, “For me, it depends what I eat and how much. Some foods I notice as soon as I’ve swallowed; others take one to three hours to digest before I feel sick. Benadryl usually does the trick for the panic, swelling, and itchiness. Sometimes my stomach and GI are in agony for several hours. I’m always better by the next day.”

Other members have symptoms for longer: “I usually feel symptoms for seven to 10 days after, depending on which allergen I ate.”

Another member wrote, “Mine can last up to eight weeks, but it depends how bad I am. Usually the normal is three weeks.”

Talk With Others Who Understand

MyFoodAllergyTeam is the social network for people with food allergies and their loved ones. On MyFoodAllergyTeam, more than 39,000 members come together to ask questions, give advice, and share their stories with others who understand life with food allergies.

What kind of food allergy reactions have you experienced? How long did your symptoms last, and did you require medical attention for severe symptoms? Share your experience in the comments below, or start a conversation by posting on your Activities page.

    Updated on November 1, 2023
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    Shruti Wilson, M.D. is an allergist and immunologist in Burlington, Massachusetts. Learn more about her here.
    Anastasia Climan, RDN, CDN is a dietitian with over 10 years of experience in public health and medical writing. Learn more about her here.

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