Autoimmune diseases and allergies

Sometimes people have an intolerance to certain foods, with lactose intolerance being the most common example. An intolerance is different in that the immune system is not involved. The reaction is usually limited to the digestive tract, with unpleasant but not severe symptoms such as diarrhoea or nausea. 

A food intolerance is different to a food allergy in that it does not always cause an immediate reaction but may occur hours after the food is consumed or build up gradually over time. It is also often possible for a person with a food intolerance to consume small amounts of the offending substance, whereas with an allergy even a tiny amount of the allergen is enough to trigger the immune system reaction. 

Both autoimmune diseases and allergies often occur when a person has a genetic predisposition; in other words, they run in families. Milk allergy, for example, is more common in children whose parents also have allergies. Celiac disease, an autoimmune disorder related to the body’s reaction to gluten, occurs almost exclusively in people with a certain genetic variant. However, less is known as to why the allergy or autoimmune disease is triggered in some people and not in others, even when they have a genetic predisposition. 

One of the key differences between autoimmune diseases and allergies is that allergies can appear and disappear, especially in children, whereas autoimmune disorders are generally lifelong conditions. The symptoms also tend to be completely different. For example, allergies produce a sudden shock to the system, while autoimmune disorders cause progressive damage to tissues and organs within the body if left untreated.  

The exact cause of autoimmune diseases remains unknown. One possible theory is that some microorganisms (bacteria or viruses) or drugs may trigger changes that confuse the immune system. In many cases, it also seems to be true that people have genetic predisposition to developing a given autoimmune disorder, as is the case with celiac disease.   

Another theory is that allergies may trigger autoimmune diseases in a way that it still not properly understood. Researchers have made a connection between walnut allergy and an autoimmune disease that affects the skin called pemphigus vulgaris. Exposure to the walnut allergen in some individuals seemed to act as a trigger for the skin disease.   

Many more discoveries remain to be made regarding the immune system and what triggers allergies and autoimmune diseases.