Pityrosporum folliculitis or Malassezia folliculitis is a skin condition caused by infection by pityrosporum yeast.:314
The skin of the upper trunk area like the back, arms and sometimes the neck is often affected and this condition is often seen in young to middle aged adults, although it has been known to occur in adults well into their sixties, and can also be found on the lower extremities as well. Its diagnosis is based on the pruritic (itchy) papulopustules found in a follicular pattern in these regions.
White pustules form from an overgrowth of the yeast, Malessezia furfur, plugging the follicles. M furfur is lipophilic, requiring fatty acids like what is present in oily skin to proliferate. It is part of the normal flora found on the skin, but overgrows in those that have a propensity for its growth. Overgrowth is associated with oily skin, humidity or other pre-existing dermatologic conditions like seborrheic dermatitis and severe dandruff.