Final answer:
Lichen planus is an autoimmune reaction, not a virus, bacteria, or fungus, and is not contagious. It belongs to the same broad category of conditions as multiple sclerosis and rheumatoid arthritis, which involve the immune system attacking the body's own tissues.
Step-by-step explanation:
Lichen planus is an autoimmune reaction that affects the skin, producing lesions and mucosal involvement. It is not a virus, bacteria, fungus, nor is it contagious. It is often characterized by purple, itchy, flat-topped bumps on the skin. Autoimmune diseases such as multiple sclerosis, diabetes mellitus type I, and rheumatoid arthritis can have varying symptoms and manifestations but share the commonality of the body's immune system erroneously attacking its own tissues.
Unlike conditions such as viruses (e.g., varicella-zoster, rubella) and bacterial infections (e.g., Lyme disease), autoimmune reactions represent a malfunction of the body’s immune system, rather than an external pathogen attacking the body. Lichen planus, similar to systemic lupus erythematosus, involves an immune response that leads to an inflammatory reaction in the skin or mucous membranes.