Measuring a porokeratosis lesion on the leg of a 69 year old white man. This chronic condition causes patches of dry, discoloured skin with a well-defined border. The patches are normally a few centimetres in size but may slowly enlarge over time. In most cases they are asymptomatic, however, in around 7% of cases they become cancerous. Porokeratosis typically does not require treatment, although to improve the appearance of the lesions, topical drugs, laser therapy and cryotherapy (freezing) can be employed. For an image of this lesion undergoing the cornoid lamella ink test see C060/2891 to C060/2892.