Malassezia is a type of fungus or yeast that grows naturally on your scalp. In some people malassezia begins to grow uncontrollably, causing a variety of symptoms, including itching.
A number of factors can contribute to an overgrowth of yeast on your scalp. These include hormonal changes, stress, Parkinson's disease and other neurological disorders, and immune-system suppression.
In addition to itching, malassezia causes dandruff or white flakes on your scalp. If the yeast infects your hair follicles, it also might cause a pink rash or bumps on your scalp.
The diagnosis of malassezia normally requires only a physical examination by your doctor, explains the Mayo Clinic.
Anti-dandruff shampoo and topical antifungal medications such as ketoconazole or ciclopirox are common treatments for an itchy scalp due to a yeast over-production, reports the New Zealand Dermatological Society. If your hair is very thick and difficult to treat with topical ointment, your doctor also might prescribe the oral form of ketoconazole or another anti-fungal medication, itraconazole.
Shampooing regularly, and avoiding styling products that can irritate your skin, such as mousse and gel, can help treat scalp problems, suggests the Mayo Clinic.