human
What is the most common cause of a rash on the chest and back?
assistant
The most common cause of a rash on the chest and back is a viral infection. Common viruses that can cause this type of rash include chickenpox, mononucleosis, shingles, and roseola. Other causes of a rash on the chest and back include contact dermatitis from certain soaps, detergents, or jewelry; allergic reactions to medications, food, or insect bites; and skin conditions such as eczema, psoriasis, and lichen planus.