Peanut allergy: symptoms, diagnosis and living with it

A food allergy is caused by the immune system overreacting to a particular food. The NHS lists peanuts among the most common allergic foods, alongside cows' milk, eggs, tree nuts, shellfish and wheat. In peanut allergy the reaction is triggered by the protein in peanuts, and Allergy UK notes that even tiny traces of peanut protein can cause a reaction in very sensitive people.

Peanut is botanically a legume, like peas and lentils, and belongs to a different plant family from tree nuts such as almonds, cashews or walnuts. Allergy UK points out that a peanut allergy does not automatically mean tree nut allergy, but roughly 30 to 40% of children with peanut allergy will be allergic to at least one tree nut, and it also raises the likelihood of sesame allergy.

Reactions usually appear within minutes of contact, though Allergy UK says they can occur up to an hour later. Most are mild to moderate, but any reaction has the potential to be severe, and allergy tests cannot predict how severe a future reaction will be.

The NHS describes anaphylaxis as a life-threatening allergic reaction that happens very quickly. It says to call 999 if lips, mouth, throat or tongue suddenly swell, if breathing is very fast or difficult, if the throat feels tight or swallowing is hard, if skin or lips turn blue, grey or pale, or if someone becomes suddenly confused, drowsy, faint or floppy.

• Mild to moderate: itchy mouth, hives, swelling of the lips or around the eyes, nausea, vomiting, tummy pain, runny nose.

• Severe: swollen tongue or throat, hoarse voice, wheeze or persistent cough, noisy breathing, dizziness, collapse.

• In babies: looking pale, floppy or suddenly sleepy can be a sign.

The first step is a GP, who may arrange testing or refer to a specialist allergy service. Allergy UK describes skin prick testing and specific IgE blood tests to peanut as the usual methods, used alongside the history to judge whether a food allergy is likely. The NHS adds that a supervised diet in which the food is avoided, and a food and symptoms diary, may also be used.

Allergy UK cautions against alternative testing methods that are not recommended by healthcare professionals, as they can be unreliable and lead to foods being removed unnecessarily. It also says that if peanuts have been avoided because of concern, they should not be reintroduced without medical advice.

Allergy UK summarises research showing that delaying peanut introduction can increase the risk of allergy. Infants at higher risk, such as those with early-onset or moderate to severe eczema or an existing food allergy, may benefit from introducing egg and peanut from around 4 months alongside other complementary foods, and this is best discussed with a health professional.

Infants without eczema or known food allergy can have peanut once solid food begins, at around 6 months and when developmentally ready, but not before 4 months. It should be given as smooth peanut butter or peanut snacks made for babies, never whole peanuts or crunchy peanut butter because of the choking risk. Allergy UK also says it is safe for pregnant and breastfeeding women to eat peanuts unless they are allergic themselves.

Because there is currently no cure, complete avoidance is the mainstay. That means reading ingredient lists, asking about food in restaurants, and being aware that peanuts can appear in cereals, baked goods and many cuisines. Unrefined peanut oil may still contain protein and Allergy UK advises avoiding it, and also advises avoiding refined peanut oil because it is difficult to be certain it is refined enough. Cross-contamination at home can be reduced by cleaning surfaces and utensils thoroughly and using separate containers for spreads.

An individual allergy action plan completed by a health professional lists the allergens, signs of a reaction and what medicines to give. Allergy UK notes the MHRA recommends two adrenaline devices for people at risk of anaphylaxis, which should always be carried, and that those with allergic asthma are at increased risk of a severe reaction so keeping asthma well controlled is important. Not everyone with food allergy needs adrenaline; that decision is made individually. A needle-free adrenaline nasal spray has been licensed for some age and weight groups, though Allergy UK says NHS availability is currently limited.

Allergy UK describes oral immunotherapy, where small and gradually increasing amounts of peanut are eaten under specialist supervision to raise tolerance. It stresses that this should never be tried without medical supervision, and that it remains the subject of research programmes, with research suggesting it is safest and most successful in younger children. The NHS says children with peanut allergy may have immunotherapy to become less sensitive, but should still avoid eating peanuts.

Other approaches, including omalizumab, sublingual immunotherapy and skin patches, are described as available only through clinical research programmes or the private sector. These options change quickly, so any decision belongs with an allergy specialist who knows the current licensing and local provision.