Mildly erythematous mucosa means that mucous membranes appear somewhat red, according to Health Tap. The redness usually signifies inflammation or irritation. Diffuse, in medical terminology, means not localized or concentrated, says the Merriam-Webster Medical Dictionary.
Most spaces in the body and internal organs are covered by mucous membranes or mucosa, explains Health Tap. There are several possible causes for Irritation or inflammation of mucosa, including auto-immune disorders, toxic agents, trauma and infections. To diagnose on the basis of diffuse mildly erythematous mucosa, various aspects require consideration, such as its locations in the body, when it began, and what might have precipitated its occurrence.