Many people with food allergies have an allergic reaction within a few minutes of eating a food allergen. Almost all reactions happen within two hours of exposure to proteins in foods like shellfish or tree nuts. However, in some rare cases, an allergic reaction to food can take hours to appear.

No matter when symptoms start, using medication prescribed by your treatment team as soon as you notice a reaction 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 Respond Quickly to Epinephrine

Allergic reactions to food are usually treated with epinephrine auto-injector shots, such as an Auvi-Q or EpiPen, or an epinephrine nasal spray (Neffy). These powerful medications are the quickest way to reverse an allergic reaction.

Epinephrine enters the bloodstream and, within minutes, helps to:

• Reduce swelling
• Decrease hives
• Stabilize blood pressure
• Help with breathing problems
• Minimize gastrointestinal (GI) symptoms

Epinephrine shots are most effective when you use one shortly after being exposed to a food allergen. Waiting too long to treat an allergy can increase the risk of death from anaphylaxis (a severe allergic reaction). After giving an epinephrine shot, always call 911 or seek emergency medical care.

Another Reaction Can Happen Hours After Exposure

Sometimes, even after epinephrine treatment, food allergies can cause a biphasic reaction — a second wave of symptoms. The first reaction may subside, but a new round of symptoms can appear and require additional care. This second reaction usually happens one to four hours after the first, but in some cases it can happen up to 48 hours later.

Studies show that between 1 percent and 20 percent of people with food allergies may experience a biphasic reaction, and there’s no way to predict who will be affected. One study from 2021 found that 8.9 percent of people had a biphasic reaction after having an anaphylactic reaction. This is why it’s so important to seek emergency medical care after a severe allergic reaction.

How Long Does It Take Treatment To Work for Mild Symptoms?

For less severe food allergy symptoms, you may be able to use antihistamines or other medications called H1 or H2 receptor blockers. Because they need to go through the digestive system first, these treatments take longer to work than epinephrine, which (outside the hospital) is usually injected intramuscularly (into the muscles) or subcutaneously (under the skin).

Antihistamines mainly help treat mild skin symptoms like itching or hives. Some start working within about 15 minutes. Diphenhydramine (sold under various brand names, including Benadryl) takes between 15 and 60 minutes to work, and cetirizine (Zyrtec) takes about 15 to 30 minutes. Both are sold without a prescription. Diphenhydramine is approved for children ages 6 and older, though a doctor may recommend it for younger children in certain instances. Cetirizine is approved for children 2 and older.

One MyFoodAllergyTeam member wrote, “I always carry two EpiPens and Benadryl. … EpiPen is only used if I am lying on the floor struggling to breathe. I had my allergy diagnosed when I was 9 years old, and I am now 71. I’ve used an EpiPen only once, and it saved my life.”

Asthma inhalers with albuterol can also help with symptoms like trouble breathing and coughing. Just keep in mind that these treatment options are not an alternative to epinephrine. Check with your doctor to make sure over-the-counter treatments are right for you or your child’s food allergies.

When To Seek Emergency Care

Although oral medications can help with some mild symptoms, they can’t replace the lifesaving injections needed to treat anaphylaxis. Use epinephrine right away if you have the following symptoms:

• Abdominal pain
• Repeated 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 in case of a severe allergic reaction.

If you’re showing symptoms of anaphylaxis, especially difficulty breathing, dizziness, throat tightness, tongue swelling, or repeated vomiting, you may need an ambulance to the emergency room. Tell the dispatcher if you’ve already injected epinephrine or taken another allergy medication.

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

How Long Will Symptoms Last Without Treatment?

There isn’t much research on how long food allergy symptoms last without treatment. Symptoms also may not improve on their own. If you have a known food allergy, do not wait. Untreated symptoms can lead to a life-threatening anaphylactic reaction. Treating symptoms right away gives you the best chance of staying safe and avoiding the emergency room.

How much of the food allergen you ate can affect how severe your symptoms are. Allergy testing can help identify your specific food triggers so you know what to avoid and when to treat reactions. If your doctor decides your allergy is severe enough that you need an epinephrine auto-injector, don’t hesitate to use it during an emergency. The risks of using the auto-injector when it’s not needed are far smaller than the risks of not using it during anaphylaxis.

If it’s been a long time since your last allergic reaction, you might wonder if you still need to take precautions. To find out if you’ve outgrown a food allergy, see an allergist. The allergist may order skin prick tests, blood tests, or they may supervise you during an oral food challenge. Oral food challenges include a period where you are watched for a reaction, with emergency care nearby.

How To Avoid Continued Exposure

Unlike people with environmental allergies, like hay fever, who may need ongoing treatment, people with food allergies can avoid their triggers and stay prepared for accidental exposures. Follow up with your healthcare provider if your symptoms aren’t improving or seem to be getting worse despite treatment.

Symptoms of an allergic reaction can range from tingling in the mouth to severe nausea, vomiting, and shortness of breath. Even if you’ve had reactions in the past, every reaction can be different, and can cause new and unexpected symptoms.

To avoid future exposure to your food allergens, you’ll need to read food labels, choose 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 for avoiding your food allergens.

Treating Food Allergies To Prevent Future Reactions

Scientists are developing new immunotherapies intended to reduce the risk of severe food allergy reactions. Some of these therapies involve regular, carefully controlled exposure to tiny amounts of an allergen to help the immune system become less sensitive over time.

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 triggering allergic reactions. By binding to and neutralizing IgE, biologic drugs may help prevent the processes that lead to severe allergic reactions and life-threatening anaphylaxis.

In February 2024, the U.S. Food and Drug Administration (FDA) approved omalizumab (Xolair) to reduce the risk of severe allergic reactions after exposure to a food allergen. It’s the first FDA-approved treatment that can be used for several food allergies. However, it is not meant to treat anaphylaxis or symptoms of 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 everyone differently. While you can learn about the most common food allergy symptoms and responses to treatment, hearing real-life experiences may help you relate to others facing similar challenges.

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 panic, swelling, and itchiness. Sometimes my stomach and GI system are in agony for several hours. I’m always better by the next day.”

“For me, it depends on 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.”

— A MyFoodAllergyTeam member

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

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

“I usually feel symptoms for seven to 10 days, depending on which allergen I ate.”

— A MyFoodAllergyTeam member

Join the Conversation

On MyFoodAllergyTeam, people share their experiences with food allergies, get advice, and find support from others who understand.

What kind of food allergy reactions have you experienced? How long did your symptoms last, and did you require medical attention for severe symptoms? Let others know in the comments below.