The most common STDs that cause a generalized rash are syphilis or AIDS, while the others do not cause a generalized rash. Syphilis can develop all over the body, but also on the head, face, trunk, and extremities, and can be a red rosacea or dark rash. AIDS can cause seborrheic dermatitis and itching all over the body, but itching does not cause a rash, and other manifestations of the skin all over the body can occur, but only finger flaking alone.