The reasons why people develop a food sensitivity are ultimately unknown. There is a strong genetic association in the development of certain food intolerances and coeliac condition. For instance, the prevalence of lactose intolerance is very high (around 90%) among adults of Chinese or Afro-Caribbean origin compared to 5% in Northern European adults. Similarly, coeliac condition has a strong genetic link. If one member of a family has the condition, there is roughly a 1 in 10 chance that other family members will develop the condition as well. The condition mostly affects Caucasian populations at about 1% of the total population. However, the reasons why the condition goes on to develop in susceptible individuals have still not been determined.

Many people with food allergy also suffer from asthma, eczema, hay fever, dermatitis or other allergies or these ‘allergic diseases’ are prevalent in their families. The tendency within a family to develop allergic disease is called ‘atopy’ and any combination of these allergic diseases can occur in an atopic family. These diseases can aggravate the symptoms of food allergy: for instance if asthma is not controlled by medication it can make allergic reactions to food more severe.

Since the 1950s, food allergies have become increasingly common in developed countries. For example, peanut allergy – the food allergy most likely to cause life-threatening reactions – has trebled in the last 12 years. In the UK, peanut allergy now affects almost 2% of children starting primary school. Overall, food allergy affects an estimated 2-3% of adults and 5-8% of children. While no hard data is available for the island of Ireland, it is assumed that rates are similar to those in the UK.