Corynebacterium minutissimum, which produced coral-red fluorescent porphyrin, thrives on moist keratinous lesions such as are seen in intertriginous eruptions of the feet and groins. Its role seems secondary rather than primary. While antibacterial soap usage readily reduces its numbers and often removed fluorescence of the skin, there is poor clinical correlation with either of these factors.
Classical erythrasma was not investigated in this study. It is our belief that coral-red or red fluorescent intertriginous scaling and fissuring should not be considered "erythrasma," even though C minutissimum is found in both situations. This diagnosis should be preserved for the classical clinical lesion.
Burns RE, Greer JE, Mikhail G, Livingood CS. The Significance of Coral-Red Fluorescence of the Skin. Arch Dermatol. 1967;96(4):436-440. doi:10.1001/archderm.1967.01610040086017