Does dandruff happen because someone does not wash their hair?

Dandruff. A yeast called malassezia. This fungus is one of the normal microscopic life forms that grow, along with certain bacteria, in your skin's oily secretion (sebum). Creams, foams or lotions containing an antifungal agent, such as ketoconazole (ketozole, extina), often help reduce flare-ups, supporting the idea that this yeast is a contributing factor. But seborrheic dermatitis is not contagious.