An abnormal redness and inflammation of the skin caused by the congestion and dilation (widening) of the capillaries (tiny blood vessels). The effect is usually localized or patchy. In layman's terms, erythema is a skin rash. Some references include the mucous membranes as well as the skin in their definition. Additional Info: Rashes have many different causes such as heat, drugs, ultraviolet rays, ionizing radiation, over-exposure to sunlight and/or allergic reactions. The term "erythema" is often used in conjunction with other words or modifiers to indicate a very specific type of rash. For example, erythema multiforme refers to a skin rash that results from an allergic reaction. MSDS Relevance: As far as an MSDS is concerned, erythema most often indicates a rash that forms as a result of skin contact with the material (See: Contact Dermatitis). Therefore, it is important to avoid contact of such materials with the skin, mucous membranes or eyes. Use appropriate personal protective equipment (PPE) such as gloves, aprons, goggles, dust masks etc. as necessary to prevent contact or exposure. See also: Dermatitis, Edema, Lesion, Urticaria, Vesicant