Experimental folliculitis with Pityrosporum orbiculare: the influence of host response.

The aetiology of the folliculitis associated with seborrhoeic eczema is unclear, though the yeast, Pityrosporum orbiculare has been implicated. P. orbiculare was applied under occlusion to normal forearm skin of patients with seborrhoeic eczema (SE), seborrhoeic eczema and folliculitis (SEF), and normal controls. There were significant differences in response to occlusion between the three groups. Those patients with previous clinical evidence of folliculitis (SEF) developed folliculitis at the site of occlusion more frequently than either of the other two groups (p less than 0.001), in whom only one patient developed skin changes. This difference was not explained by the response to occlusion alone, nor by natural carriage of yeasts. These results suggest that the yeast P. orbiculare is necessary for the development of folliculitis, but that the nature of the host response determines those patients prone to follicular inflammation.