Pathogenic fungi are fungi that cause disease in humans or other organisms. The study of pathogenic fungi is known as "medical mycology." Although fungi are eukaryotic organisms, many pathogenic fungi are also microorganisms. Superficial infections are caused by fungi that attack the skin or its appendages (nail, feathers and hair). Some examples of these infections include ringworms, jock-itch and athlete's foot. These fungi are known as dermatophytes, as they cause damage to the skin. The infection will occur below the skin, but will remain localized. Fungi invade and grow in dead keratin. Keratin is a protein that makes up your skin, hair and nails.