erythrasma is a superficial infection caused by corynebacterium minutissimum and affects the major skin folds and the interdigital regions of the feet it is characterized by erythematous brown scaly patches and maceration and exhibits coral red fluorescence under wood light the aim of this study was to determine the frequency of erythrasma in patients with interdigital lesions an open prospective longitudinal observational study was performed in a hospital in mexico city between march and december 2006 all patients with interdigital lesions were examined with a wood lamp and direct examination was performed with 20 potassium hydroxide cultures were done in sabouraud dextrose agar and brain heart infusion agar and smears were analyzed general characteristics and concomitant diseases were recorded we examined 73 patients of whom 24 32 8 were diagnosed with erythrasma based on coral red fluorescence under wood light and identification of corynebacteria by gram staining the disease was more common in women 83 33 and the mean age of the patients was 43 5 years the main clinical findings were scaling and maceration and the fourth interdigital web was the most commonly affected corynebacterium could not be isolated in any of the cases mycology was positive in 15 cases 62 5 and the following microorganisms were isolated candida 16 6 dermatophytes 12 5 and trichosporon 4 1 interdigital erythrasma is a common condition and can be easily confused with interdigital tinea it persists if not treated appropriately rapid diagnosis is easily obtained by examination with a wood lamp while culture is difficult and unnecessary for diagnosis the coexistence of erythrasma with dermatophytes and candida should be considered when the interdigital webs are affected.