A 29-year-old man comes to the clinic for recurrence of an intensely pruritic rash in his groin over the past 6 months. He reports temporary improvement with an over-the-counter antifungal cream, but the rash returns within a few weeks after he stops treatment. He showers daily and denies new soaps or detergents. He works in a warehouse and sweats heavily. Physical examination shows erythematous, scaly plaques with a slightly raised border on the medial thighs and inguinal folds. Examination of the feet shows interdigital scaling and maceration between the 4th and 5th toes bilaterally. Which of the following best explains the recurrence of this patient’s groin rash?