Medical photography, and in particular dermatological imagery, is often assumed to provide an objective, and functional, representation of disease and that it can act as a diagnostic aid. By contrast, artistic conceptions of the images of the body tend to focus on interpretative heterogeneity and ambiguity, aiming to create or explore meaning rather than enact a particular function. In her 2015 retrospective exhibition at the Tate Modern, South African artist Marlene Dumas questions these disciplinary divides by using medical imagery (among other photographic sources) as the basis for her portraits. Her portrait 'The White Disease' draws on an unidentified photograph taken from a medical journal, but obscures the original image to such a degree that any representation of a particular disease is highly questionable. The title creates a new classification, which reflects on disease and on the racial politics of South Africa during apartheid. Though, on the one hand, these techniques are seemingly disparate from the methods of medical understanding, features such as reliance on classification, and attempts at dispelling ambiguity, bring Dumas' work closer to the history of dermatological portraits than would usually be perceived to be the case. In considering the continuities and disparities between conceptualisations of skin in dermatology and Dumas' art, this paper questions assumptions of photographic objectivity to suggest that there is greater complexity and interpretative scope in medical dermatological images than might initially be assumed.