• Skin rashes - eczema (atopic dermatitis) or hives (urticaria)
• Swelling - angioedema
• Sneezing and running nose - allergic rhinitis (hay fever)
• Teary, red, itchy eyes - allergic conjunctivitis
• Asthma
• Nausea and vomiting - food allergy
• Anaphylaxis - severe allergic reaction, which causes serious breathing problems and can be life threatening.

Medical issues to consider
Before the allergy tests, you need to discuss a range of issues with your doctor, including:

• Medical history
• Clinical symptoms and when they occur
• Possible allergen triggers
• Any medicines you take that may interfere with skin prick test reactions, such as antihistamines.

The procedures
Specific tests are required to determine exactly which substance or substances are causing the allergy. These tests include:

• Skin prick tests - selected allergens are applied to the forearm or back with a dropper, and the skin gently pricked with a needle. A positive result shows within 20 minutes as a red weal or flare.
• Allergen-specific IgE blood tests (RAST) - are useful when skin testing is impossible or skin tests are inconclusive. After a blood sample is taken, the level of allergen-specific IgE (an immunoglobulin associated with allergic reaction) produced is measured in a laboratory.
• Elimination diets and challenge testing - an elimination diet is used to isolate foods that may be causing an allergic reaction for a particular person. It usually takes a number of weeks, and involves avoiding foods that have been identified as common causes of food allergy. No foods or fluids may be consumed other than those specified in the starting diet. If symptoms improve, foods are added one at a time until symptoms occur. Usually, a diary is kept to record any symptoms so they can be linked to the correct food. This procedure must only be performed under medical supervision.
• Patch tests - are most commonly used to investigate contact dermatitis. Common triggers include fragrances (in soaps, for example), nickel (in jewellery, watch buckles and coins) and chrome (in leathers and bricklayers' cement). The reagents are available as patches arranged along adhesive strips. The strips are applied to the back. The area is examined after two and four days. A positive result shows as redness or blisters at the site of a particular reagent.