en Dermatology Dermatology Original Research Original Research <p> <strong>Abstract</strong></p><p> <strong>Background:</strong> Psoriasis is a chronic proliferative condition of the skin. Its accurate pathogenesis has not been known yet, but interactions between genes and environmental factors have been implicated in its initiation. The role of malassezia in psoriasis is still undetermined, but several reports have associated these lipophilic yeasts with the development of skin lesions in psoriasis.Our aim was to investigate the correlation between malassezia and psoriasis.</p><p> <strong>Methods:</strong> In this case control study over a 6 month period skin samples were obtained from lesions of 50 psoriatic and 50 healthy volunteers to evaluate malassezia infestation. Obtained data were collected by questionnaires and analyzed by SPSS software and applying statistical tests of χ2 and Mann-Whitney.</p><p> <strong>Results:</strong> There was no difference between malassezia infestation in scalp lesions of psoriatic and control cases (P=0.86). Malassezia infestation in psoriatic patients with scalp involvement was more than those without it, but it was not a significant relationship (P=0.069). There was an inverse significant correlation between scalp infestation with malassezia and chronicity of psoriasis (P=0.04). This infestation in trunk skin of patients was less than normal individuals (P<0.000).</p><p> <strong>Conclusion:</strong> There seems to be an initiating role in inducing immune mechanisms involved in the pathogenesis of scalp psoriasis by malassezia, but with chronicity and formation of dry and hyperkeratotic plaques, the environment will be inappropriate for malassezia, so malassezia infestation decreases with chronicity of disease.</p> psoriasis, malassezia , etiology 11 16 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-1-145&slc_lang=en&sid=1 Z Javidi zari_javidi@yahoo.com 20031947532846002002 20031947532846002002 Yes Department of Dermatology, Imam-Reza Medical Center, Mashhad University of Medical Sciences, Mashhad, Iran. Maleki 20031947532846002003 20031947532846002003 No Department of Dermatology, Imam-Reza Medical Center, Mashhad University of Medical Sciences, Mashhad, Iran Fata 20031947532846002004 20031947532846002004 No Department of Laboratory Sciences, Imam-Reza Medical Center, Mashhad University of Medical Sciences Nahidi 20031947532846002005 20031947532846002005 No Imam-Reza Medical Center, Mashhad University of Medical Sciences Esmaeili 20031947532846002006 20031947532846002006 No Health & Social Medicine Dept., Quaem Medical Center, Mashhad University of Medical Sciences Hosseini 20031947532846002007 20031947532846002007 No