Hazard Identification

Peanuts are unrelated to tree nuts such as almonds and hazelnuts, and actually develop in a seed-pod below ground, which explains their alternative name -- goundnuts. They are also sometimes called monkey nuts. Botanically, peanuts are a member of the legume family, which includes peas, soya beans and lentils.

Peanuts are one of the most common causes of food allergy and can cause severe reactions, including anaphylaxis. Very tiny amounts of peanut can cause a reaction in people who are sensitive. An adverse reaction to peanuts is a true food allergy response, involving an over-reaction of the immune system and production of IgE antibodies.

Allergenicity

Peanuts are harvested as shelled products containing the fruit surrounded by a skin and formed into two halves. Peanut proteins make up about 25% of the fruit, and it is these proteins that are responsible for peanut allergenicity. Peanut proteins are thought to contain numerous allergenic fractions, many of which still remain unidentified and uncharacterised. Neither roasting nor other heat treatment of peanuts seems to reduce the allergenic response. In fact, roasting peanuts may actually increase their potential allergenicity. This is quite unusual, as most allergenic proteins can be made less allergenic, or non-allergenic, by heat treatment. On the other hand, when peanuts are boiled in water, their allergenicity is reduced. This is because some of the allergenic proteins leach out into the cooking water.

Prevalence

Peanuts are a common cause of food allergy in the USA, where consumption of peanuts is very high. Peanut allergy is also becoming increasingly common in the UK in line with the increasing popularity of peanut products. Although exact numbers are unknown, some studies suggest that one person in 200 might be affected to some degree, although a recent study in children, carried out in 2002, indicated that as many as one in 70 children across the UK was allergic to peanuts. At one time, it was thought that peanut allergy was life-long in all cases, but recently it has been shown that about 20% of young children outgrow their peanut allergy.

It is thought that the increased incidence of peanut allergy is the result of increased dietary exposure to peanuts at an earlier age than previously occurred. Susceptible infants can probably become sensitised through breast-feeding, via certain ointments used for skin lesions, or via the respiratory system following exposure to peanut allergen. Sensitisation may even occur in utero. Atopic individuals with asthma seem to be more at risk of developing food allergies.

Hazard Characterisation

Effects on health

The symptoms of peanut allergy can vary tremendously, from very mild to severe. The most common mild symptoms include:

• Tingling in the mouth and lips and facial swelling.
• Nausea and colicky pain, accompanied by a feeling of tightness in the throat.
• Urticaria or nettle rash.

Severe reactions, exhibited by those more sensitive to peanuts include:

• Swelling of the airways and obstructed breathing.
• Sudden drop in blood pressure.
• Collapse and unconsciousness.

These symptoms result from the widespread release of pre-formed histamine and other inflammatory mediators from mast cells and basophil cells. The more severe reactions are classified as anaphylaxis and require immediate medical attention. The onset of anaphylactic reactions is generally extremely rapid and can proceed very quickly to unconsciousness.

A recent analysis was carried out of 32 fatal cases of food-related anaphylaxis reported to a national registry, established by the American Academy of Allergy, Asthma, and Immunology, with the assistance of the Food Allergy and Anaphylaxis Network. The 32 individuals could be divided into 2 groups. Group 1 had sufficient data to identify peanut as the responsible food in 14 (67%), and tree nuts in 7 (33%) of the cases. In group 2 subjects, 6 (55%) of the fatalities were probably due to peanut, 3 (27%) to tree nuts, and the other 2 cases were probably due to milk and fish. The sexes were equally affected; most victims were adolescents or young adults, and all but one subject were known to have a food allergy before the fatal event. In those subjects for whom data were available, all but one was known to have asthma, and most of these individuals did not have epinephrine available at the time of their fatal reaction. In this series, peanuts and tree nuts accounted for more than 90% of the fatalities.

Dose-response

The amount of peanuts required to elicit an allergic reaction has not been extensively studied, although sensitive individuals can react to minute amounts (100µg -- 50 mg). Some case studies report reactions to extremely low doses of peanut. For example, children have been reported to exhibit symptoms after contact with a table, reportedly wiped clean of all visible peanut butter; other cases have been documented as being caused by kissing someone who had previously eaten peanuts, or by sharing drinks. Symptoms were even reported by a patient when a jar of peanut butter was opened in their presence. Even being close to someone eating peanuts can be sufficient to cause a reaction in some individuals.

Management of peanut allergy

Complete avoidance of peanuts and all peanut products is the best way to manage peanut allergy, although this may not be straightforward. The presence of 'hidden' peanut products in processed foods is always a risk for sensitised individuals. Food labels must always be read carefully as peanuts and their products may appear under different names, such as groundnuts, monkey nuts, earth nuts, mixed nuts, peanut butter, peanut oil, groundnut oil and arachis oil. Products such as cakes, biscuits, desserts, ice cream, cereal bars, satay sauces, breakfast cereals, ready meals (particularly Thai, Indonesian, Chinese and Indian meals), curry sauces, salad dressings, marzipan and praline and vegetarian products such as veggie-burgers, etc. may all contain hidden peanut products.

Eating out in catering establishments and buying unwrapped foods also pose a risk, as no labelling laws exist to cover these situations. Care is needed in preparation and storage of food to ensure that no cross-contamination occurs.

It is probably wise for children who are allergic to peanuts to avoid other nuts, sesame seeds, nut mixes and possibly other legumes to prevent further sensitisation.

Sources of Further Information

Published

Sampson HA.
Clinical practice: Peanut allergy.
New England Journal of Medicine, 2002, 346(17),1294-1299

On the web

The Anaphylaxis Campaign
www.anaphylaxis.org.uk/

British Nutrition Foundation fact sheet
http://www.nutrition.org.uk/upload/Peanut%20Allergy.doc

The InformAll Database
http://foodallergens.ifr.ac.uk/

Food Allergy Info website (Institute of Food Research)
www.foodallergens.info