These reactions can occur in the skin (irritation and itching) and can also have more severe expressions (bronchial asthma and anaphylactic shock). Mouth and skin expressions are a sign that differentiates an allergy involving IgE from an intolerance to some type of food.

The types of food that most frequently cause allergies are milk and eggs in children and fish and dried fruit in adults. However, allergies against any food can occur. Sometimes allergens are substances carried by food (like Anisakis simplex, a parasite of fish) instead of the food itself.

Food types related to each other can share the same allergen. This explains reactions against several different foods. The main groups are:

• Carrots, celery, anise, apple, potato
• Cereals: wheat, rye, barley, oats, maize, rice
• Hake, salmon, trout, tuna
• Garlic, onion, asparagus
• Peas, lentils, licorice, soy, beans, hazelnuts and fennel
• Peach, apricot, plum, banana
• Prawn, crab, lobster, squid

There also are associations between other allergens and food:

• Grass pollen and peaches
• Birch pollen and apples
• Mugwort pollen and celery
• Feathers of parrots and canaries and eggs
• Latex and avocado, banana, chestnut, kiwi, walnut, peach.