A 32-year-old man comes to clinic for an itchy rash that has been worsening for 3 months. He reports greasy “dandruff-like” flaking that is most noticeable after not washing his hair for a few days. He also notes redness and flaking around the eyebrows and along the hairline. He has no fever, joint pain, or oral ulcers. Physical examination shows erythematous plaques with greasy yellow scale on the scalp and eyebrows. Which of the following is the most likely underlying etiology of this patient’s condition?