Malassezia is a genus of fungi (specifically, a yeast belonging to the division Basidiomycota).

Some species of Malassezia are found on the skin of animals, including humans. Because malassezia requires fat to grow, it is most common in areas with many sebaceous glands—on the scalp, face, and upper part of the body.

Malassezia infections of human skin can cause or aggravate a variety of conditions, including dandruff, seborrheic dermatitis, and acne.

When Malassezia grows too rapidly, the natural renewal of cells is disturbed, and dandruff can appear with itching (a similar process may also occur with other fungi or bacteria).

Identification of Malassezia on skin has been aided by the application of molecular or DNA-based techniques. These investigations show that M. globosa is the species that causes most skin disease in humans, and that it is the most common cause of dandruff and seborrhoeic dermatitis (though M. restricta is also involved).

There can be as many as ten million M. globosa organisms on a human head.

A project in 2007 sequenced the genome of dandruff-causing Malassezia globosa and found it to have 4,285 genes. M. globosa uses eight different types of lipase, along with three phospholipases, to break down the oils on the scalp. Any of these 11 proteins would be a suitable target for dandruff medications.

Prescription and over-the-counter shampoos containing ketoconazole are commonly used to treat dandruff caused by Malassezia.