A 34-year-old man comes to clinic for an intermittently itchy, flaky rash that has been worsening for 6 months. He notes prominent “dandruff” that does not improve with regular shampoo. He also has greasy scale and mild erythema around the eyebrows and in the nasolabial folds. He is otherwise healthy and takes no medications. Physical examination shows thin, erythematous plaques with yellowish, greasy scale along the scalp margin and eyebrows. Which of the following best describes the underlying etiology of this patient’s condition?