Individuals with reaction to specific allergens to foods, inhalants or substances can be known to develop allergy to others and it is becoming better recognised that reactions are occurring to different foods containing either the same allergen, or an allergen with a very similar protein structure. Reactions can be either light or heavy and this is known as allergic cross-reactivity.

This means that someone may suffer an allergic reaction even when they're avoiding the foods they know they're allergic to. If someone is allergic to peanuts, for example, they might react to soya, peas, lentils or beans which are food items in the same biological family (legume). Allergic cross-reactions can also happen between certain fruit or vegetables and latex (known as latex-food syndrome), or the pollens that cause hayfever.

If a person has a measurable reaction to a certain food with clinical diagnosis, advice to avoid similar foods that could trigger this reactionmight be helpful.

The most well-documented cross-reactivity is the one which occurs between apple and birch pollen. Nevertheless, individuals allergic to apple are not necessarily allergic to birch pollen. Cross-reactivity should not be assumed and important foods be eliminated from the diet without appropriate testing and clinical diagnosis.

Aniseed Light Mugwort Birch, weeping
Apple Medium Birch, weeping Celery, Cherry, Cocksfoot, Mugwort,
peach, Pear, Potato,
Ragweed - common,
Rye-grass, Tomato
Alder Pollen Medium   Almond, Apple, Celery,
Cherry, Hazelnut, Parsley,
Peach, Pear
Ash, Common Light Birch, weeping; Lilac, common; Olive  Privet - common,
Ragweed - common,
Avocado Medium Latex  Banana, Kiwi 
Banana Heavy Latex  Abocado, Birch - weeping,
Goose-foot, Kiwi, Melon
Bermuda Grass Light Blue grass - (Kentucky), Cocksfoot,
Reed - common, Ryegrass - perennial,
Celery, Olive, Rape - oilseed,
Rye-grass, Sunflower -
Birch pollen Medium    Almond, Apple, Apricot,
Buckwheat, Carrot, Celery,
Cherry, Coriander, Fennel,
Hazel nut, Honey, Kiwi,
Nectarine, Parsley, Parsnip,
Pear, Peach, Peanut, Pepper,
Plum, Potato, Prune, Spinach,
Walnut, Wheat
Birch, weeping  Heavy Apple, Ash - common, Beech -
common, Carrot, Celery,
Chestnut - sweet,
Cob - hazel, Curry, Hornbeam - common,
Kiwi, Oak - English, Pear,
Aniseed, Banana, Elm -
Scottish, Caraway seed,
Chamomile - German,
Cherry, Coriander,
Fennel seed, Hazelnut,
Latex, Lychee, Mango,
Mugwort, Olive, Orange,
Paprika - condiment,
Parsley, Peach, Pepper,
Potato, Rape - oilseed,
Rye-grass, Soy bean,
Carrots Heavy Birch - weeping, Celery, Mugwort  Cucumber, Head Lettuce,
Mango, Melon
Cherry Light   Birch - weeping, Apple,
Chicken Egg Heavy Canary (erinus canarius), Chicken,
Duck - domestic,Goose - domestic,
Hen - domestic, Parrot - African
gray (psittacus erithacus),
Parakeet (nmphicus hollandicus)
feathers, Parakeet (Melopsittacus
undulatus), Pigeon 
Cocksfoot Grasses Heavy Bermuda grass, Blue grass -
(Kentucky), Melon, Oat flour,
Rye flour, Ryegrass - perennial,
Timothy, Vernal grass - scented 
Apple, Meado - fescue,
Oats - common, Reed -
common, Rye-grass 
Cod Fish Light   Carp, Eel, Herring, Mackerel,
Plaice, Salmon, Sole,
Tuna fish
Corn Light    Barley, Blue grass - (Kentucky),
Millet, Oats - common, Soy
bean, Ryegrass - perennial,
Rice, Wheat - common 
Crab Light    Oyster, Shrimp, Squid 
Cucumber Light Celery Carrot, Melon 
Curry Mixed Spices Medium Birch - weeping, Celery, Mugwort    
Edible Chestnut Medium Latex    
Fennel Seed Light   Birch - weeping, Celery, Mugwort 
Grape Light   Peach
Grass pollen Medium   Melon, Orange, Swiss chard,
Tomato, Watermelon,
Hazelnut Heavy Cob - hazel  Birch - weeping, Kiwi, Mugwort,
Peach, Poppy seed, Rue flour,
Kiwi Fruit Medium Birch - weeping, Latex, Timothy  Avocado, Banana, Hazelnut,
Mugwort, Poppyseed, Rye
flour, Ryegrass - perennial,
Latex Rubber Heavy Avocado, Bannana, Edible
Chestnut, Ficus benjamini
(Tropic laurel - Weeping
fig), Kiwi, Mango, Melon, Papaya, Tomato
Apple, Birch - weeping,
Buckwheat, Carrot, Celery,
Dill, Fig, Mugwort, Orange,
Oregano, Passion fruit,
Peach, Peanut, Pear,
Pineapple, Potato, Ragweed - common, Rye-grass, Sage,
Soy bean, Strawberry,
Timothy, Walnut 
Lentil Light   Pea Walnut
Lychee Light    Birch - weeping
Melon Medium Celery, Cocksfoot, Latex,
Ragweed - common 
Banana, Carrot, Cucumber, Goose-foot, Plaintain - English, Zucchini 
Mugwort pollen Medium   Carrot, Celery, Coriander, Fennel, Melon, Parsley,
Pepper, Spices, Sunflower, Watermelon 
Onion Light   Asparagus, Garlic, Timothy 
Orange Heavy    Birch - weeping 
Papaya Light Latex   
Paprika Condiment Light   Birch - weeping, Celery,
Pea Light    Lentil, Mugwort, Peanut 
Peanut Heavy Tomato  Latex, Lentil, Mugwort, Parientaria, Pea, Peach, Soy bean
Pear Medium   Apple, Birch - weeping,
Mugwort, Peach 
Pepper Light   Celery, Birch - weeping,
Pineapple Light    Latex, Rye-grass 
Poppy Seeds Light    Hazelnut, Kiwi, Rye flour
Pork Medium Cat - domestic   
Potato Light    Apple, Birch - weeping,
Latex, Tomato
Ragweed pollen Medium    Apple, Banana, Cantaloupe, Chamomile tea, Honey, Honeydew, Nuts, Sunflower, Watermelon 
Tomato Light Birch - weeping, Peanut,
Rye-grass, Timothy 
Apple, Celery, Latex,
Mugwort, Potato 
Walnut Light   Peach