Gram stain is used to categorized bacteria into gram-positive and gram-negative organisms. The basic mechanism of Gram staining is the retention of crystal violet, which is another name for gentian violet. Gram-positive bacteria and fungi retain gentian violet in the presence of an alcohol wash, while gram-negative bacteria do not retain gentian violet because the compound does not penetrate the cell wall of gram-negative bacteria. The retention of gentian violet is likely due to the formation of an adduct, which is resistant to decolorization. Recently, our research group3 demonstrated that gentian violet forms a covalent adduct with thioredoxin reductase 2, a highly conserved protein from bacteria to humans, and is likely a candidate for the retention of gentian violet by the fungus. An additional explanation for selective dye retention is alterations in either host or fungal lipids. Unaffected skin does stain with gentian violet, but the affected areas stain more intensely.