Why are allergies not classified as autoimmune diseases?

Allergies are not classified as autoimmune diseases because they do not involve the immune system attacking the body's own tissues. Autoimmune diseases occur when the immune system mistakenly identifies healthy cells as foreign and mounts an attack against them. Allergies, on the other hand, occur when the immune system overreacts to harmless substances in the environment, such as pollen, dust, or certain foods. While allergies can cause significant symptoms and discomfort, they do not involve the immune system attacking the body's own tissues, which is the defining characteristic of autoimmune diseases.