Medically, all abnormal manifestations on the skin can be called a rash, a rash. The causes of rashes are varied, and not all rashes are contagious. Infections (including bacteria, viruses, fungi, and specific pathogens), allergies, animals, parasites, medications, sunlight, physical factors, autochthonous, and immune dysfunction are all causes of rashes. Among them, infectious rashes are concentrated in the infectious and parasitic categories, but not all infectious rashes are contagious. 1, viral rash. The most common infectious rashes, most of which are transmitted through the respiratory tract and have fever symptoms before the onset, such as rubella, measles, chickenpox, scarlet fever, shingles, etc. 2. Bacterial rash. For example, impetigo, his exudate is contagious. Similarly, dengue, folliculitis, cellulitis are also bacterial infections resulting in rashes, but are generally considered non-contagious. 3. Fungal. For example, ringworm of the head, ringworm of the hands and feet, ringworm of the nails, etc., are somewhat contagious, and then, for example, furunculosis folliculitis, which is not very contagious and is generally not considered to be contagious. 4.Parasitic. For example, scabies, malignant infectious disease. Others, such as psoriasis, herpetic aspergillosis, aspergillosis-like, eczema, etc., although the rash looks serious, but not infectious. The prerequisite for contagion is the presence of a pathogen, and from this perspective, there are relatively few infectious rashes.