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A food allergy is when the body¡¯s immune system reacts unusually to specific foods. Although allergic reactions are often mild, they can be very serious. In the most serious cases, a person has a severe allergic reaction (anaphylaxis), which can be life-threatening.

Food allergy symptoms usually develop within a few minutes to two hours after eating the food. Rarely, symptoms may be delayed for several hours. Common symptoms of a food allergy include:

• Digestive problems: Nausea, vomiting, diarrhoea, abdominal pain.
• Skin reactions: Itching, hives, redness, swelling.
• Respiratory issues: Sneezing, runny nose, coughing, wheezing, difficulty breathing.
• Swelling: Swelling of the lips, tongue, throat, face.
• Cardiovascular symptoms: Rapid or weak pulse, fainting.
• Anaphylaxis: A severe, potentially life-threatening reaction involving multiple systems of the body, characterised by a drop in blood pressure, loss of consciousness, and difficulty breathing. 

Most frequent causative food is hen's egg, followed by cow's milk and then wheat (Figure1). Table 1 shows that the ranking of food allergies vary by age. In recent years, the number of tree nut allergies that develop in early childhood is increasing.

Risk factors for food allergies include:

• Family history
• Genes
• Eczema

Because eczema is the biggest risk factor for developing food allergies, skin care is important to avoid the development of food allergies.

• History taking
  History of presenting complaint /Symptoms and reactions /Ask if there are problems with specific food(s) /What triggers symptoms or reactions? / Situations leading up to the reaction /Family history, etc.
• Blood tests
  Blood tests measure the levels of specific IgE antibodies to various allergens in the blood. These tests can identify specific allergens that may trigger allergic reactions.
• Skin prick test(SPT)
  This test involves placing a small amount of allergen extract on the skin (usually on the forearm) and then pricking or scratching the skin to allow the allergen to enter. If a person is allergic to the substance, a raised, red, itchy bump will appear within about 15-20 minutes.
• Oral food challenge test(OFC)
  OFC is an examination to investigate the presence or absence of induced symptoms in a subject following the administration of a food. The objectives for OFC are
  1. Definitive diagnosis of a food allergy (identification of the causative allergen)
  2. Determination of the safe intake quantity and judgement of tolerance acquisition

The best way to prevent an allergic reaction is to identify the food that causes the allergic reaction and avoid it, however, it is important to consume as much as possible and eliminate as little as possible under the guidance of a doctor.