What are food allergies?

Food Boxes

Food allergies can be scary. In some cases they cause severe reactions. And symptoms may start very young. Babies can develop an allergy to milk, eggs or peanuts as early as six months old. But it’s important not to let fear rule. Food allergies can be managed, if you can discover exactly what your trigger is and get to know your condition inside out.

In this article, we look at the more familiar type of food allergies and some that are less common. And explain why food allergies are not the same as food intolerance.

Common food allergies

You can be allergic to any food but some food allergies are more common than others. Food packaging must make common allergens obvious in the list of ingredients. The same labelling laws cover restaurant menus. But it’s often impossible for food producers to rule out cross-contamination. That’s why you might see voluntary warnings on certain foods, such as “may contain traces of peanuts”.

These are the ingredients that are listed as major causes of allergic reactions: cow’s milk, eggs, fish, shellfish, tree nuts, peanuts, wheat and soybean. Sesame will join them in 2023.

Food allergies: It's your immune system

Around 4–6% of children and 4% of adults in the US are affected by food allergies. It starts when your immune system overreacts to proteins found in something you eat. The immune system’s job is to protect your body against bacteria or viruses that could make you unwell. But sometimes it gets it wrong. It mistakes a particular food for a threat and rushes to your defence. Your body wants to get rid of the allergen as fast as it can. That’s an allergic reaction.

How to read food labels

  • Triple check every food label: when you buy food, as you put it away at home and before you eat or serve it. It’s easy to miss something at a glance
  • Scan the packaging all over (not just the ingredients) for a “may contain…” warning and don’t take the risk if you find one
  • If you’re food shopping online look for a filter for allergies
  • Encourage even young kids to check labels for any food allergen. It makes great reading practise and soon becomes second nature
  • Tell the Food & Drug Administration (FDA) if you get food allergy symptoms but there’s no allergen on the label
  • Sign up here for FDA email alerts about product recalls due to allergen contamination. Or follow the organization on Twitter

How food allergies develop

You don’t get a food allergy the first time you eat peanuts or shellfish or whatever your trigger is. Your immune system needs to build its defenses first. It makes antibodies called Immunoglobulin E (IgE). Now you’re sensitized to that allergen. This may happen without you even realizing you’ve been exposed. It doesn’t mean you’ll definitely develop a food allergy but you could.

If you do, the IgE antibodies will fight back whenever you meet the allergen. They’ll tell other cells to release chemicals like histamine. Various fluids and white blood cells also travel to the site of the supposed attack to help. Pretty quickly you’ll feel the typical symptoms of an allergic reaction.

How fast can you get food allergy symptoms?

Many people realize they’re having an allergic reaction within minutes or even seconds. And most symptoms show up within two hours.

One exception is a rare type of allergy to red meat that starts after a tick bite. The tick’s saliva can sensitize you to lamb, pork, beef and venison. Allergy symptoms tend to start four to eight hours after a meal and can be severe.

There’s another rare type of food allergy where the allergic reaction can start more slowly too – days later sometimes. Read more about non-IgE-mediated food allergy below.

Typical food allergy symptoms

Allergic reactions to food can range from mild to severe. These are some of the symptoms to look out for:

  • Tingling or itching in the mouth
  • A raised, itchy red rash (hives) – sometimes the skin can turn red and itchy but not raised
  • Swelling of the face, mouth, throat or other parts of the body
  • Difficulty swallowing
  • Wheezing or shortness of breath
  • Feeling dizzy and lightheaded
  • Feeling sick (nausea) or vomiting
  • Abdominal pain or diarrhea
Find a doctor search icon
Find a doctor
Need help managing your food allergy? Maybe it’s time to see a doctor near you

The same person can react differently on different occasions. You may feel a bit unwell one time but need immediate medical treatment another. That’s why it’s important to see your healthcare provider if you suspect you may have a food allergy.

Food allergies: what is a severe allergic reaction?

Have you heard of anaphylaxis (pronounced an-a-fi-LAK-sis)? It’s a sudden and severe and often sudden allergic reaction that can be life-threatening. Having this type of reaction once increases the chances of it happening in the future. So does a family history of severe reactions and having asthma or allergies. Call 911 if you spot the warning signs and symptoms of anaphylaxis:

  • Skin reactions, including hives and itching and flushed or pale skin
  • Low blood pressure (hypotension)
  • Constriction of your airways and a swollen tongue or throat, which may cause wheezing and trouble breathing
  • A weak and rapid pulse
  • Nausea, vomiting or diarrhea
  • Dizziness or fainting

Some people can get these symptoms if they play sports after eating a food they’re allergic to. It’s called food dependent exercise related anaphylaxis and luckily it’s fairly rare.


Don’t change your diet without talking to your healthcare provider. They’ll work out a treatment plan with you. That’s likely to be avoiding your triggers and treating any symptoms.

Symptoms of non-IgE-mediated food allergies

This type of food allergies do not involve IgE antibodies. Protective white blood cells called T cells lead the allergic reaction. Symptoms often affect your skin and your digestion. You may get heartburn, indigestion, vomiting or diarrhea hours or even days after eating.

Non-IgE-mediated food allergy symptoms are not usually severe but they can make children reluctant to eat. And that increases the risk of developing other health issues over time. Conditions include:

  • Pollens from trees, grasses or weeds
  • Waste particles from house dust mites
  • Molds
  • Certain foods such as nuts, dairy, shellfish
  • Pet dander
  • Insect stings

In mixed IgE and non-IgE-mediated food allergies both mechanisms play a part. You may also get both types of symptoms.

Food allergy symptoms or cross-reaction?

Certain fruit, vegetables, nuts and spices can make your lips tingle without being your main allergy trigger. The root cause is actually pollen allergy. That’s why this type of cross-reactivity is called pollen food syndrome (PFS). Another name is oral allergy syndrome (OAS). It happens because the food contains a protein very like the one in your problem pollen. Say ragweed pollen gives you hay fever. Well, you might get a mild local reaction in your lips, mouth, or throat when you eat cucumber.

People might experience pollen food syndrome when eating foods such as almonds, hazelnuts, peanuts, and soybeans. But these are also major causes of food allergy. So talk to your healthcare provider straightaway if it happens.

There is also a rare type of cross-reaction between cat allergens and pork. It usually happens quickly, has the same symptoms as IgE food allergies and can be life-threatening. It’s a reaction called pork-cat syndrome.

Woman wondering about the difference between skin prick and blood allergy tests.

How does allergy testing work?

So how do I find out if I have food allergies?

Allergy testing is often the first step. That might be a skin prick test which involves putting a drop of liquid containing the allergen or a diluted sample of the fresh food onto your arm, pricking the skin underneath it gently and checking for a reaction. Or you may need an allergy blood test to look for IgE antibodies. This will show if you’re sensitized to any food allergens. The healthcare provider will ask about your symptoms and family history before making a diagnosis. It can be helpful to keep food and symptom diary.

Non-IgE-mediated food allergies are harder to diagnose. Your healthcare provider may suggest an oral food challenge. This involves giving you increasing amounts of an allergen while watching for symptoms. Or they may want to do an internal examination with a camera (endoscopy). It depends on your medical history.

Food allergies are not the same as food intolerances

Allergy testing can’t tell you if you have a food intolerance. That’s when your body struggles to digest a substance such as histamine, lactose, or gluten. It’s nothing to do with the immune system.

Food intolerance symptoms are usually mild to moderate. They also tend to start more slowly than with food allergies. You may even find you can eat a small amount of the problem food without feeling unwell. In food allergies, a tiny trace can cause a reaction. The usual way to diagnose a food intolerance is with an elimination diet. But there are breath and blood tests to identify lactose intolerance.

An expert guide
to food intolerance

Food allergies are different to intolerance which gives some people, like this woman on her sofa, tummy ache after drinking milk

How to manage food allergies

Don’t change your diet without talking to your healthcare provider or allergist. They’ll work out a treatment plan with you. This is likely to be a mixture of avoiding your triggers and treating the symptoms when you haven’t been able to.

Antihistamine blocks the effect of the histamine your body releases as part of an allergic reaction. It is a common treatment for milder allergy symptoms. Ask your pharmacist for advice about the different types available over-the-counter.

If your healthcare provider thinks you’re at risk of a severe reaction they’re likely to prescribe an auto-injecting adrenaline pen to carry with you at all times. You could also think about wearing an allergy necklace or bracelet so people know how to help you in an emergency.

Food allergies: 6 ways to avoid your triggers

We’ve talked about how to read food labels to help avoid common food allergy triggers – that is, very carefully. And the importance of teaching children to do the same. There are other good habits to get into that can help reduce the risk of having an allergic reaction both at home and on the go.

  1. Check non-food products: Skincare, cosmetics, petfood, vitamins, even modelling clay and finger paint can all include food allergens.
  2. Be allergy aware when eating out: Get in touch with the restaurant beforehand to discuss exactly what you need from them not to have an allergic reaction. Help-yourself food counters like salad bars are best avoided. Other customers may have double-dipped the cutlery in something you’re allergic to.
  3. Plan ahead when you travel: Tell the airline about your food allergies and order a special meal if you can. On trains and buses take your own food. Pack allergy medications in carry-on luggage in case of emergencies (plus spares in your suitcase). It’s sensible to have both your prescription and a doctor’s letter on you; you may need to explain why you’re carrying meds. Breathing in food allergens is unlikely but you could pick them up on your hands from tables or armrests. So bring cleaning wipes. Translation cards or an app may help you identify allergens in a foreign country.
  4. Take care in the kitchen: Avoid cross-contamination. Store food for someone with allergies on its own shelf and label containers. Clean surfaces, pots and pans, utensils and the microwave with a disposable wiper. Allergens can linger on sponges. Try always to eat at the table. And of course always wash your hands.
  5. At school: Create an allergy action plan with your child’s school or care provider. And make sure your child knows all the forms of food and drink their allergen could appear in. Give them the confidence to ask adults about a food if they’re in any doubt. And to ask for help if they start feeling unwell – including with vomiting or diarrhea.
  6. Allergens exist in saliva too: Studies suggest that traces of peanut can linger in saliva for a few hours. So never share cutlery or drinking cups if you have food allergies. And at the risk of spoiling that first kiss, tell your date about your allergy first.

The best general rule is to wash your hands with soap and water before eating or putting your hands near your face. And any time you think you may have been in contact with allergens.


Kids can outgrow food allergies and you can sometimes get them for the first time in later life too. Grown-ups often mistake their symptoms for food poisoning.

Is there a cure for food allergies?

You may be thinking of allergy immunotherapy. It’s not a cure but it can greatly reduce your symptoms. This long-term treatment tackles the root cause of allergy. Repeated tiny doses of the allergen gradually desensitize your immune system so it doesn’t react in the same way.

Food allergies can be trickier to treat than pollen or dust mite allergy because of the risk of severe allergic reactions. But oral immunotherapy is now available for peanut allergy from the age of four. The goal is to desensitize you to an accidental exposure to peanuts to help prevent a severe reaction.

Food allergy in children

Children may outgrow allergies to milk and other common early triggers such as eggs, soy and wheat. But peanut and tree nut allergy are more likely to stay with you into adulthood.

One way to help prevent food allergies starting in the first place may be to introduce babies to peanuts and other trigger foods much earlier. Allergy experts think starting from six months old or before might encourage the immune system to accept the allergens in later life. Talk to your healthcare provider or allergist first, especially if food allergy runs in your family or your baby has eczema (atopic dermatitis). Both make it more likely a child could develop food allergies.

Food allergy in adults

Your immune system goes on learning and adapting to new threats throughout your life. This means your allergy can change too. There’s a name for it – the allergic march. Just as kids can outgrow food allergies, grown-ups sometimes get them for the first time too.

The most common triggers for adults are shellfish and fish as well as peanuts and tree nuts. People having their first allergic reaction later in life often think it’s food poisoning. But you know now that vomiting and diarrhea can be symptoms of food allergy too. So why not speak to your doctor just in case.

Share your story
If you’ve read all the way to the end of this article, thank you. We’d love to know what you think. If you have any questions or would like to share your story of living with food allergies, email us or head over to our Facebook page.
klarify takes allergy science and makes it simple, and we have rigorous process for doing this. We use up-to-date and authoritative sources of information. Medical experts review our content before we share it with you. They and the klarify editorial team strive to be accurate, thorough, clear and objective at all times. Our editorial policy explains exactly how we do this.