Xeroderma Pigmentosum and Porphyria Genetic diseases, caused by the crippling of chromosomes before birth. The skin develops no melanine so that there is no protection from UV light and its agressive rays. The person suffering from these deseases easily get burned in the sun up to 3rd degree or produce skin cancer after spending only minutes in the day/sunlight. As bad as this might be for them, it has nothing to do with vampirism. Vampires can go out during the day but mostly avoid it as it is not their natural time, therefore uncomfortable and weakening. There are some interesting facts that should be take into consideration when comparing vampirism to this genetic malfunction. First, those suffering from any of those diseases are also easily burnt by artificial light and are forced to spend a life in nearly total darkness. Second, they don«t crave for blood or any other kind of energy. Third, they are all born with this genetic defect Porphyria and XP are not infective. A thesis of some researchers, why they are related to vampirism as well, is that due to the incestive attitude of some European regions during the earlier centuries and also the aristocratic families, this disease may have occured extremely often in some regions of the world, therefore was more present and watchable for the normal population. And everyone can easily imagine what a Romanian farmer of the 18th century might have thought when he watched someone being slowly burnt by the sun.