Common food allergens

Peanuts and tree nuts

Peanuts can turn up under the names groundnuts, earth nuts and monkey nuts. It is important to read food labels thoroughly, even if you are buying a product you have eaten before. Recipes do sometimes change. Check both the inner and outer wrapping of multi packs.

Foods most likely to contain peanuts or tree nuts include:

• Cakes, biscuits, pastries, ice cream, desserts.

• Cereal bars, confectionery.

• Vegetarian products such as veggie burgers.

• Salads and salad dressings.

• Satay sauce, curries, Chinese, Thai or Indonesian dishes.

• Marzipan and praline (confectionery products made with nuts).

• Salad dressings may contain unrefined nut oils.

The above list is not exhaustive.

Foods sold in restaurants and other catering outlets, or at in-store bakery and delicatessen counters, are generally unlabelled and so pose a particular problem. It's important to be direct with staff, pointing out the seriousness of the allergy. If staff cannot guarantee that any dish is safe, it is best to eat elsewhere.

Peanuts (arachis hypogaea) are actually legumes. A small percentage of people with peanut allergy react to other legumes, such as peas, beans and lentils. Care is needed, but most will find they can tolerate these other legumes without problems. More commonly, people with peanut allergy react to tree nuts. Many allergy experts advise peanut-allergic patients to avoid tree nuts, and vice versa.

Sesame seeds

Sesame allergy is fairly common in some countries and it would appear to be on the increase in the UK. Occasionally reactions are severe. Even when these are mild or moderate, it must be assumed that a future reaction may be severe and medical advice should be sought in all cases.Sesame is often used for flavouring and decorative purposes in foods. People who are allergic to sesame must seek to avoid it completely, as even a tiny amount may trigger a severe reaction.

Dishes containing sesame include: tahini, gomashio, hummus and halvah. Chinese stir fry oils sometimes contain sesame oil. Sometimes it is to be found in Aqua Libra.

People have also reported allergic reactions to vegeburgers, breadsticks, burger baps, cocktail biscuits, Middle Eastern foods, Chinese and Japanese foods, stir fry vegetables and health food snacks containing sesame.

Sesame oil should be regarded as extremely risky because it is almost certain that it will be unrefined, and therefore contain the allergenic proteins that trigger allergic reactions.

Bread and other products bought from in-store bakeries must also be viewed as suspect because these may be contaminated by sesame seeds from other bread.

Sesame is sometimes used in cosmetics and other personal care products and in such cases may be labelled under the Latin name sesamum indicum. Sesame oil may occasionally be present in pharmaceuticals. Always ask your pharmacist to obtain full ingredients of any prescribed medicine.

Egg allergy

Egg allergy - common among children - is usually mild. But in rare cases egg can trigger anaphylaxis. Food labels must be thoroughly scrutinised for products containing egg or albumen.

The emulsifier known as lecithin can be derived from egg, although in practice this is uncommon. If you in doubt about any product, it is best to contact the retailer or manufacturer.

Some egg-allergic children can eat well-cooked egg (in cake, for example) without any ill effects - but not raw or lightly cooked egg. Others are allergic even to egg which has been well cooked. People who are fine with cooked egg are more likely to grow out of egg allergy.

A lot of fresh pasta contains egg, but you will certainly be able to find a dried pasta that is egg-free. Some varieties may occasionally carry a very small risk of cross-contamination with egg. Check with individual companies to identify the safe ones.

The MMR injection is normally cultured on egg. Anaphylactic reactions to the MMR have been reported, but they are very rare. In any case, it's probable that in those instances, a component other than egg was responsible. Any child who has a severe allergic problem, irrespective of whether this is due to egg or not, should at least be reviewed by a paediatrician in order to consider whether the immunisation should be administered in a controlled environment.

Cow's milk allergy

The term cow's milk allergy is generally used to describe reactions generated by the immune system. This is how the term will be used here. Non immune reactions are normally classified as cow's milk intolerance.

Cow's milk allergy is common in infants and very young children. It rarely develops after one year of age and the onset is closely related to the introduction of cow's milk based infant formula. The prevalence is estimated to be as high as two per cent among children under a year old. Fortunately about half outgrow their allergy by one year, and most children have outgrown it by the age of three. However, cow's milk allergy may occasionally be lifelong and severe.

A food does not have to be eaten to cause a reaction, although eating it causes more severe reactions. Hives can occur on skin contact with milk. If food gets into the wet surfaces (e.g. through a cut in the skin, on the lips or in the eye) severe reactions can occur.

Inhaled cow's milk protein, such as from the cheese on a pizza, can cause allergic reactions. These are not normally severe unless present in extremely high concentrations.

Degrees of avoidance will depend on the individual and the severity of the milk allergy. Many people need to avoid milk and dairy but can cope with trace amounts in cooked goods (e.g. cakes, biscuits and pies).

Milk can turn up unexpectedly in foods so it is important to check food labels every time you shop - even if you have bought a product before. Recipes do sometimes change. Some medicines contain milk products so check with the prescribing doctor or with the pharmacist when collecting your prescription.

Lactose does not normally contain the proteins responsible for causing reactions, but there is a risk of contamination with milk protein. People with very severe milk allergy may be wise to avoid anything with lactose in it.

Apart from the obvious ingredients to avoid (such as milk, cream and dairy) watch out for the following:

• Butter, butter fat, buttermilk, butterfat, butter oil.

• Casein, whey.

• Sodium caseinate and calcium caseinate.

• Cheese, yoghurt, ghee.

• Ice cream.

People who are allergic to milk react to the milk protein and not to the milk sugar (lactose). Lactase deficiency is quite different and caused by the lack of the enzyme lactase, which is needed to digest lactose.

Soya milk formulae are sometimes recommended for infants who are allergic to cow’s milk however, some milk-allergic children react to soya.

Goat’s milk and sheep’s milk are usually not suitable alternatives to cow’s milk as they share similar proteins with cow’s milk that could result in cross-reactivity.

Shellfish and fish allergy

Adverse reactions to shellfish are rare in young children, and are usually not seen until the teenage years or adulthood. This may be a reflection of the fact that shellfish is not normally a part of the diet of young children.

Allergy to fish - such as cod and other white fish - may begin in childhood and is likely to be lifelong. Allergies to shellfish or fish are potentially serious and there may be a rapid onset of symptoms.

Someone who reacts to one type of fish - even if the symptoms are mild - might be advised to play safe and eliminate all fish from their diet. This is partly because they may react to another type of fish, but also because of the high risk of cross-contamination among different types of fish (e.g. at fish markets or on fish counters).

This also applies to shellfish. People allergic to one type of shellfish are often advised to avoid all shellfish.

Biologically speaking, shellfish are aquatic invertebrates rather than fish. They can be divided into four main groups:

Crustaceans (e.g. crab, lobster, crayfish, shrimp, prawn)

Molluscs:

a) Bivalves (e.g. mussels, oysters, scallops, clams)

b) Gastropods (e.g. limpets, periwinkles, snails)

c) Cephalopods (e.g. squid, cuttlefish, octopus)

People who have reacted to one type of shellfish (e.g. crab) are likely to react to other members of the same group (in this case, other crustaceans). Shellfish from the other groups may not necessarily present a problem, although they may do for some people. It is advisable to avoid them anyway as there is a relatively high risk of cross-contamination among different types of seafood.

Fish and shellfish are biologically distinct. People who are shellfish-allergic may be able to eat fish, and vice versa - unless they have both allergies. But as stated above, be aware of the risk of cross contamination in restaurants, markets and open fish counters.

In restaurants, inform staff of your allergy. Find out what your food is fried in, and whether the oil has been used for anything else. Check the ingredients of all stocks and soups. Ideally, your companions should avoid eating fish/shellfish in your presence, as there is a small risk that breathing in the cooked food may cause a reaction.

Dishes to look out for include paella, bouillabaisse, gumbo, frito misto, and fruits de mer. Oriental food tends to contain lots of different kinds of fish at once, and chopped pieces can be difficult to spot.

Although it is the flesh of shellfish that contains the allergen, people with shellfish allergy are advised to avoid shellfish shells and skeletons.