Allergy is defined as an immune-mediated inflammatory response to common environmental allergens that are otherwise harmless. The diagnosis of allergy is dependent on a history of symptoms on exposure to an allergen together with the detection of allergen-specific IgE. The detection of allergen-specific IgE may be reliably performed by blood specific testing or skin prick testing. Skin prick testing is not without its attendant risks, and appropriate precautions need to be taken. A doctor should be present for safety and test interpretation. Accurate diagnosis of allergies opens up therapeutic options that are otherwise not appropriate, such as allergen immunotherapy and allergen avoidance. Allergen immunotherapy is an effective treatment for stinging insect allergy, allergic rhinitis and asthma. The most effective methods for primary prevention of allergic disease in children that can currently be recommended are breastfeeding and ceasing smoking. Emerging trends in allergen treatment include sublingual immunotherapy.