What's the difference between allergies, intolerance, and sensitivity?

The word “allergy” is commonly used when any adverse reaction to food, drugs, or other substances happens. However, the word “allergy” only truly applies when IgE-primed mast cells release histamine and other chemicals in response to a normally harmless substance (the allergen).

Intolerance is often encountered when dealing with foods. It occurs when a person lacks the correct enzymes to digest the food. An example of such a condition is lactose intolerance. People who are lactose intolerant cannot digest lactose, a type of sugar found in milk and dairy products. The lactose passes into the large intestine undigested and the bacteria break it down, releasing gas, which can cause the feelings of bloating, pain, wind, and diarrhoea. This is not an allergy as no immune cells are involved.

Sensitivities are technically not allergies because IgE-primed mast cells are not involved, however, they are not intolerances either, as the individual has the appropriate enzyme for digesting whatever it is they are sensitive to. An example of sensitivity is Coeliac disease. IgE is not involved, but other immune cells participate. This leads to the gut's absorptive surface shrinking, and food cannot be absorbed as well. This food passes into the large intestine where bacteria break it down.

Allergies Guide Index:

• What are allergies?
• What's the difference between allergies, intolerance, and sensitivity?
• Overview of the immune system
• How do allergies happen?
• Who gets allergies?

• What are some common symptoms of allergies?
• What are some common allergies?
• How can I check to see what I'm allergic to?
• What treatment options are available?