Sporotrichosis is caused by a species of fungus; this fungus differs from the superficial fungi (dermatophytes) responsible for the varieties of Tinea described in the chapter on fungal infections.

Sporotrichosis starts at the site of a minor skin wound caused by a briar, thorn, splinter, or a cut that is contaminated by vegeta­tion or soil. Barberry, rose bushes, sphagnum moss, and soil are most often associated with this infection in humans. A pustule or knot develops at the site three to twelve weeks later; the knot usually ulcerates to form an open sore. Subsequent knots develop in a linear pattern up the arm, following the lymphatic channels. These knots are lymph nodes, which sometimes soften and break open.