Malassezia yeasts have been found in human dandruff, deep-sea vents, and pretty much everywhere in between. The skin of most if not all warm-blooded animals is covered with these microbes, and while they mostly live in peaceful co-existence with their hosts, they can cause serious diseases in humans and animals. While treatments exist for most of these, when treating Malassezia skin diseases, one should always bear in mind that Malassezia yeasts are integral components of the skin microbiota, and therefore the therapeutic target should be controlling the Malassezia population rather than eradicating it.
Malassezia bloodstream infections are less common, but premature infants and immunocompromised patients with extended stays in intensive care are at risk. Such infections are often linked to catheterization that facilitates internalization of the yeasts, either from the patient’s own skin or from someone else’s. Because routine tests in patients with blood infections of un-known origin often do not detect Malassezia right away, diagnosis might be delayed, which can be dangerous. However, once Malassezia is identified as the culprit, therapy with antifungal drugs is usually successful in eliminating the pathogen from the bloodstream.
Humans are covered from head-to-toe with Malassezia. Healthy skin is actually cultivated by a well-balanced mix of bacteria and fungi (yeasts and molds), and this “skin flora” does not appear to elicit defense reactions by our immune system. How Malassezia interacts with other skin microbes is not yet known, but researchers think that both changes in the flora and changes in the immune system can disturb this peaceful equilibrium and lead to a range of skin diseases.