“Dandruff can result from dry skin, a buildup of oils on the scalp, sensitive and irritated skin, or, very commonly, an overgrowth of a fungus called Malassezia globosa,” Saedi explains, noting that it can affect both oily and dry scalps. Dr. Kobets explains that factors such as stress (which can raise cortisol levels, increasing scalp oiliness and suppressing the immune system), poor diet (one that is heavy on processed foods and sugars which causes inflammation in the body and scalp), sweating, and warmer temperatures (such as those experienced in summer or during sports) can exacerbate dandruff.