Nuts and peanuts can cause allergic reactions, which are sometimes severe. A severe reaction to nuts is called anaphylaxis and can be life-threatening. Symptoms often start quickly, within an hour of coming into contact with a nut, and sometimes within minutes. If you have a nut allergy, avoiding foods that contain nuts will prevent an allergic reaction. But, if you do come into contact with nuts, and a reaction starts then treating it quickly is important. If you have a severe allergic reaction, if available, give yourself an adrenaline (epinephrine) injection straightaway and call an ambulance. If you are well prepared and take action quickly the risk of suffering any serious problems is small.
What is nut allergy?
An allergy occurs when your body's immune system, which normally fights infection, overreacts to a substance called an allergen. Most allergens are not obviously harmful and they have no effect on people who are not allergic to them. Allergic reactions to allergens can vary from mild to life-threatening.
Both peanuts and tree nuts (for example, walnuts, hazelnuts, almonds, cashews, pecans, Brazils and pistachios) can act as allergens, and can cause an allergic reaction in some people. When you come into contact with something that you are allergic to (an allergen), a group of cells in your body, called mast cells, release a substance called histamine. Histamine causes the tiny blood vessels in the tissues of your body to leak fluid which causes the tissues to swell. This results in a number of different symptoms.
Strictly speaking, peanuts are not nuts, they are legumes, in the same family as peas and beans. Peanuts grow underground whereas other nuts grow on trees. The word nut in this leaflet can mean either tree nuts or peanuts.
What causes nut allergy?
If you are allergic to nuts, when you first come into contact with nuts your immune system reacts and prepares to fight. However, you don't get any symptoms of a reaction. It is only when you come into contact with nuts for a second time that a full allergic reaction happens. Most children who are allergic to nuts have the symptoms of an allergic reaction when they appear to be exposed to nuts for the first time. However, this is probably not their first exposure, but their second. They may already have come into contact with nuts through their mother, through either of the following:
- Whilst they were in the womb (uterus).
- Through breast milk if they were breast-fed.
Most people with nut allergy react after contact with small amounts (less than one nut) and some people may react to trace amounts. This means that you don't always have to eat nuts to have a reaction. A few people are so sensitive to nut allergens that a tiny amount on their lips, or even standing next to someone eating peanuts, can be enough to start a reaction.
There are lots of different allergens but nuts cause some of the strongest and most severe reactions. Doctors don't yet know why this is.
How common is nut allergy and who gets it?
In the UK about 2 in 100 children and about 1 in 200 adults have an allergy to nuts. The number of people with peanut allergy is growing.
Nut allergy is the most common type of severe food allergy. It often starts when children are very young. Most first allergic reactions take place when a child is between 14 months and two years old. Unlike other food allergies such as milk allergy, nut allergy is something that you are unlikely to grow out of. Only about 1 in 5 people with a nut allergy will grow out of it, and these tend to be the people who have mild reactions.
If you have what is called atopy, or if atopy runs in your family, then you are more at risk of developing an allergy to nuts. Atopy is the name for a group of allergic conditions that include hay fever, asthma and eczema. In particular, children who have eczema are more likely to develop a nut allergy. If you have an allergy to peanuts then you may also react to tree nuts.
What are the symptoms of a nut allergy?
Both peanuts and tree nuts can cause allergic reactions. Allergic reactions to nuts can vary from mild to very severe, and are sometimes life-threatening. Symptoms often start very quickly, within an hour of having come into contact with a nut, and sometimes within minutes. Reactions that take place more than four hours after coming into contact with nuts are unlikely to be an allergy.
Signs and symptoms of a mild allergic reaction can include:
- Your mouth and lips tingling.
- Your face swelling.
- Feeling sick.
- Nettle rash, or hives (urticaria).
- Colicky pains in your tummy (abdomen).
- A feeling of tightness around your throat.
Signs and symptoms of a more severe allergic reaction can include:
- All of the above.
- Wheezing or difficulty breathing due to an asthma-like attack, or swelling around your throat.
- A sense of impending doom.
- Dilation (opening up) of your blood vessels, which can cause:
- General redness of your skin.
- A fast heart rate.
- Low blood pressure, which can cause you to feel faint or to collapse.
This severe reaction is called anaphylaxis and without quick treatment you would soon become unconscious. A small number of people die every year as a result of this kind of severe reaction, usually because they do not obtain treatment quickly enough. If you think you are having an anaphylactic reaction you need to call an ambulance straightaway and obtain immediate medical help.
About 1 in 3 people with a nut allergy have an initial reaction to the nut, followed by a second reaction between one and eight hours after the first. This is why it is important to stay in hospital after an initial anaphylactic reaction.
How is nut allergy diagnosed?
Medical history and examination
Your doctor may suspect that you have a nut allergy from your symptoms. Your doctor may then ask a lot of questions. For example, the amount and type of food that you ate which caused a reaction, how quickly the symptoms started, how severe they were, how long they lasted, etc.
Skin prick test
A skin prick test may be done to help confirm the allergy. For this test, a drop of nut extract solution is placed on the skin, usually on the forearm. Then, a needle prick is made through the drop. This is usually painless as just the very surface of the skin is pricked. However, it is enough to let a tiny amount of solution into your skin. If a reaction occurs, it happens within 20-30 minutes.
- A reaction is considered to be 'positive' when the skin under the solution becomes red and itchy. A white, raised swelling called a wheal surrounds the red central area. A wheal takes about 15-20 minutes to reach its full size, and then fades over a few hours.
- A reaction is considered to be 'negative' when the skin remains normal. This means that you are not allergic to the substance in the solution.
Do not take antihistamines on the day of the test as they may dampen any allergic response during the test.
You may also have a blood test. This measures the amount of a protein called IgE antibody which is produced as a result of an allergic reaction. You can read more about IgE reactions in the separate leaflet called Food Allergy and Intolerance
If other tests are not conclusive then your doctor may ask you to take part in a food challenge. For this test you are given foods to eat that may or may not contain nuts. You will then be watched closely for 15-30 minutes to see whether you have a reaction. Food challenges are always done at a hospital or specialised setting because of the risk of a severe reaction.
If you are found to be allergic to one type of nut, you may be tested for allergy to other nuts as well. If you have an allergy to peanuts, you are more likely to have an allergy to tree nuts than a person who does not have a peanut allergy. Once an allergy has been confirmed, an allergy specialist will usually help you to devise a plan to manage it. This plan will be individual to you and will take into account how severe your reaction is.
What are the treatment options for nut allergy?
Avoid nuts wherever possible
Preventing an allergic reaction from happening in the first place is a key part of living with a nut allergy. So, learn to recognise foods that may contain nuts and avoid them. You may be referred to a dietician to help with this. Advice may include:
1. Check the ingredients:
- Always check food labels, even for products you know, as ingredients can change.
- Avoiding whole nuts is relatively easy. What is more difficult is avoiding nuts in processed foods. Nuts are not always obviously listed on ingredient labels. For example, peanut can be listed as groundnut, earth nut, monkey nut, mixed nuts, peanut butter, peanut oil, arachis oil and groundnut oil.
- Nuts and nut oils are used as ingredients in a wide range of foods. Take care with biscuits, cakes, pastries, desserts, ice cream, breakfast cereals, cereal bars, nut butters and spreads, confectionery, vegetarian dishes and salad dressings.
- Chinese, Thai and Indonesian dishes often use nuts and nut oil, particularly peanuts or peanut oil.
- Get a list of nut-free foods from your local supermarket.
2. Take care when you are not preparing your food:
- When eating out, ask staff which foods contain nuts and the risk of contamination of other foods. If possible, speak to the chef, not the waiter or waitress.
- Avoid eating foods at buffets or from delicatessens or bakeries where it is easy for food to be contaminated by touching other foods containing nuts.
- Do not eat anything you are unsure about.
- If friends or family prepare food for you, make sure they know what you can't eat.
- If your child has an allergy to nuts then make sure that they do not share food with other children at parties and other group events. Take food for them.
Principles of treatment
It is unlikely that you will always be able to avoid contact with nuts and you may be accidentally exposed to nuts at any time. So, be prepared:
1. Make sure that you, and others around you like your friends and family, know that you are allergic to nuts and what to do if an allergic reaction starts:
- If your child has a nut allergy then make sure that anyone else who looks after your child knows about it and knows what to do if a reaction starts. For example, nursery staff, babysitters, teachers and other parents. Your doctor - either your GP or a hospital doctor with special training in children's medical care (a paediatrician) - will be able to write a care plan. This care plan will tell anyone looking after your child what they should do if the child has an allergic reaction.
- You should (or your child should if they have an allergy) wear a medical emergency identification bracelet or equivalent that tells other people about the allergy.
2. If an allergic reaction starts, get the right treatment quickly:
- It is vitally important that if an allergic reaction starts you get treatment as quickly as possible. The sooner your reaction is treated, the better.
- Mild reactions can be treated with an antihistamine medicine.
- More serious reactions are treated with adrenaline (epinephrine) which, if given quickly, can reverse the symptoms of the reaction.
- Adrenaline (epinephrine) is given by an injection so that it can work straightaway. If you have a severe reaction to nuts you will be given an adrenaline (epinephrine) injection (like a pen). You will carry this with you all the time. Brand names include EpiPen®, Emerade® and Jext®.
- These adrenaline (epinephrine) injections come in different doses for adults and children. They work by injecting adrenaline (epinephrine) into your thigh muscle when you press a button or jab it against your skin.
- If you have a severe allergy you must carry your adrenaline (epinephrine) injection with you at all times. Some people keep adrenaline (epinephrine) in the places where they spend most of their time. For example, they keep it at home, at school or at work. Many people carry two injections 'just in case'.
- Check the expiry date on the adrenaline (epinephrine) regularly. If it passes the expiry date, get a new one. Also, make sure that you know how to use it properly. Your family and friends should know how to use it too, in case you are not able to.
Know what to do if you have an allergic reaction
1. Mild reactions:
- Take an antihistamine tablet as soon as possible. You can buy these at pharmacies or obtain them on prescription. Antihistamines block the action of histamine, the chemical released into your body during an allergic reaction. They usually take 15-30 minutes to start working.
- If your reaction gets worse then get medical help straightaway.
2. Severe (anaphylactic) reactions:
- If you have an adrenaline (epinephrine) injection pen, use it.
- Get help and call an ambulance straightaway. If possible, always have someone with you at all times if you have a reaction, even if you need to go to the toilet. For example, do this even if you feel sick or are being sick (vomiting).
- If you have asthma and have an inhaler, use it.
- In the ambulance or at the hospital you may also be given oxygen to help your breathing, steroids to reduce any inflammation, and antihistamines to counter the allergic reaction.
- Some people may need more intensive treatment if the reaction is very severe.
Mild symptoms can last up to an hour but severe symptoms can last longer. You will need to stay in hospital until your doctor is sure you have fully recovered.
Immunotherapy (desensitisation) is a treatment where you are given tiny amounts of the allergen which is then very gradually increased over time. The aim is to build up tolerance to the allergen. This treatment has been used with some success to treat pollen and insect poison (venom) allergies. But, at present it is not widely used to treat food allergy such as nut allergy because of the risk of anaphylaxis. However, some studies have shown some promising results, and the technique is used at some very specialist centres.
Can nut allergy be prevented?
In the past, the Department of Health advised that atopic pregnant and breast-feeding mothers and their infants should avoid peanuts. However, in 2009, the Department of Health changed their advice. They found there was no evidence that eating or not eating nuts when pregnant made any difference to the chances of a child developing allergy. Since that time they have advised there is no need for pregnant or breastfeeding mothers to avoid nuts.
There is some evidence that introducing peanuts to the diet early on in the weaning process (from 6 months of age) may make a child less likely to develop an allergy to them. Obviously whole peanuts are a choking hazard, so they need to be in a form which is safe for the baby (such as peanut butter).
Anything else I need to know?
Some people with peanut allergy might also react to some vegetables (legumes) like soya, green beans, kidney beans, baked beans and green peas because these foods contain similar allergens to peanuts. Be aware that alcohol can make an allergic reaction stronger.
Will it happen again?
Once you have had one allergic reaction, you are very likely to have another because it is impossible always to avoid nuts. This can be stressful to live with. However, if you are well prepared and take action quickly, the risk of suffering any serious problems is small.
Further reading and references
Food allergy in children and young people; NICE Clinical Guideline (February 2011)
Stiefel G, Anagnostou K, Boyle RJ, et al; BSACI guideline for the diagnosis and management of peanut and tree nut allergy. Clin Exp Allergy. 2017 Jun47(6):719-739. doi: 10.1111/cea.12957.
Anagnostou K, Islam S, King Y, et al; Assessing the efficacy of oral immunotherapy for the desensitisation of peanut allergy in children (STOP II): a phase 2 randomised controlled trial. Lancet. 2014 Jan 29. pii: S0140-6736(13)62301-6. doi: 10.1016/S0140-6736(13)62301-6.
Nurmatov U, Venderbosch I, Devereux G, et al; Allergen-specific oral immunotherapy for peanut allergy. Cochrane Database Syst Rev. 2012 Sep 12(9):CD009014. doi: 10.1002/14651858.CD009014.pub2.
Food Allergy and Anaphylaxis Guidelines; European Academy of Allergy and Clinical Immunology (EAACI), 2014
Turnbull JL, Adams HN, Gorard DA; Review article: the diagnosis and management of food allergy and food intolerances. Aliment Pharmacol Ther. 2015 Jan41(1):3-25. doi: 10.1111/apt.12984. Epub 2014 Oct 14.
Consumption of peanut during pregnancy, breastfeeding, and early life and development of peanut allergy; Dept of Health, August 2009 (archived)