Seborrhoeic dermatitis and Pityrosporum ovale: cultural, immunological and clinical studies.

Seborrhoeic dermatitis is a common skin disease mainly affecting the scalp and face. The etiology of seborrhoeic dermatitis is unknown but a connection with the lipophilic yeast Pityrosporum ovale has been found in a number of treatment studies. P. ovale belongs to the normal cutaneous flora but is also an opportunistic pathogen. The purpose of these studies was to examine how the density of P. ovale changes with age, to determine the number of P. ovale in seborrhoeic dermatitis compared to controls, to study the immunological functions in patients with seborrhoeic dermatitis, to evaluate different methods of detecting antibodies against P. ovale and to describe how the patients experience their disease. The number of P. ovale on clinically normal skin decreases with increasing age. In patients with seborrhoeic dermatitis, the number of P. ovale in lesional skin was not increased compared to healthy skin in the patients or in healthy controls. A reduction of the skin surface lipids was seen in elderly healthy individuals. The lipid content on the skin in patients with seborrhoeic dermatitis was higher than in controls (p = 0.0001). Serum IgG antibodies against P. ovale measured with indirect immunofluorescence decreased parallel to increasing age in healthy individuals and no difference was found between patients with seborrhoeic dermatitis and healthy controls. ELISA with a P. ovale protein extract was the only method that demonstrated a difference in immune response between patients and controls when this method was compared with four other assays (p = 0.03). Immunological screening was done in 30 patients with seborrhoeic dermatitis. No major abnormalities in the humoral and local immune system were found but T-cell and NK-cell aberrations were found in several patients with seborrhoeic dermatitis. One-third of the patients had low lymphocyte stimulations with Concanavalin-A and phytohaemagglutinin and almost half of the patients had high frequencies of circulating natural killer-cells. In a questionnaire answered by 431 patients with seborrhoeic dermatitis, we found indications that hereditary, the season, mental stress and the work environment influence the disease. The investigations suggest that the number of P. ovale in seborrhoeic dermatitis is of minor importance. How each individual reacts to P. ovale and the amount of skin surface lipids are probably of greater importance in the development of seborrhoeic dermatitis.