Final answer:
Contact dermatitis is a localized skin reaction caused by contact with certain substances, while immune system-mediated dermatitis refers to autoimmune diseases where the immune system attacks the body's own tissues.
Step-by-step explanation:
Contact dermatitis is a type of delayed hypersensitivity reaction that occurs when the skin comes into contact with substances such as nickel or poison ivy. It causes a localized rash or skin irritation. On the other hand, immune system-mediated dermatitis refers to autoimmune diseases where the immune system mistakenly attacks the body's own tissues, leading to conditions like rheumatoid arthritis or lupus. These diseases are more severe and widespread in the body.