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Symptoms

The symptoms of food allergies range from mild discomfort to severe, life-threatening reactions (anaphylaxis), which require immediate medical treatment. The most frequent symptoms of food allergies are itching and/or swelling of the mouth. Other symptoms include hay fever, asthma, nettle rash, and stomach upset.

The symptoms arise every time the allergic person eats the offending food. However, if they are allergic to a food that is cross-reacting with pollen they may only experience symptoms in the pollen season. 

Different kinds of food poisoning can provoke symptoms that are similar to the symptoms experienced in food allergy. Often the reaction is stronger the more poisoned food that the person has eaten. In order to distinguish between a food allergy and poisoning the person with symptoms needs to see the doctor. 

Allergic reactions to foods may occur within a few minutes after eating the offending food, but rarely symptoms may also develop after hours, making the relationship with ingestion of food less clear. Symptoms generally disappear within hours but can last for days. The specific symptoms and severity of an allergic reaction are affected by the type and amount of the allergen consumed, by the form in which the food containing the allergen was eaten, by the intake of alcohol, aspirin and other drugs such as beta-blockers and ACE inhibitors, by exercise or stress, and by the sensitivity of the allergic person. The symptoms may appear in different parts of the body:

Mouth

The most frequent symptoms of food allergies are itching and/or swelling of the mouth. Oral itching (known as Oral Allergy Syndrome) can be an initial symptom in any kind of food allergy. However, oral itching is a well known symptom in food allergy induced by cross-reaction with pollen. It can happen with foods like apple, kiwi, hazelnuts, walnuts, celery, carrot, tomato, cherry, and melon. Most of the allergens involved in pollen-related cross-reacting foods will be destroyed in the gastrointestinal tract. This explains why the symptoms are frequently mild and limited to the mouth. Most of the allergens in the cross-reactive foods will also be destroyed if the food is cooked. This explains, for example, why many birch pollen allergic people cannot eat raw apples without experiencing symptoms but stewed apples and apple juice might not be a problem.  

Eyes and nose

The eyes and nose may show hay fever-like symptoms. The eyes may swell, itch, and become red. Sneezing and an itchy and runny (or stuffed) nose may be experienced.

Lungs

Asthmatic symptoms such as wheezing, breathlessness and coughing may arise from the lungs.

Gastrointestinal tract

Symptoms from the gastrointestinal tract include pain, bloating, nausea, vomiting, and diarrhoea.

Skin

On the skin acute nettle rash (also called urticaria or hives) with itchy, well-defined white or pale red swellings can appear. This rash is generally short-lived disappearing within hours. Chronic nettle rash is rarely associated with food allergy.

Longer lasting, chronic skin reactions in the form of atopic dermatitis are associated with food allergy especially in children.

Anaphylaxis

Anaphylaxis is an uncommon, acute, potentially life-threatening and sometimes fatal allergic reaction involving the whole body. The skin itches. The affected person becomes unwell and dizzy, they feel their heart beating, they feel nauseous, and everything may go black. At the same time they may get nettle rash, hay fever, and suffer an asthma attack. Their blood pressure may drop, and they may faint. Untreated anaphylaxis can rapidly result in death.

In Europe and the US, peanut and tree nuts are the foods most commonly reported to cause life-threatening reactions. Prompt administration of adrenaline after eating suspected problem foods and transport to an Emergency Department has helped minimise life-threatening episodes.

More information

Chapter on clinical symptoms due to food allergy: