The skin is made up of 70% water, which corresponds to approximately 3 liters of water for an adult organism, and it is precisely this water contained in the skin that makes the process of skin mummification possible. Our objective is to explain the impact of mummification on the skin and the different types of knowledge that can be obtained from the study of these ancient skins through representative examples. Firstly, we carried out a bibliographical research to detail the main mummification methods in order to be able to explain the impact of these conservation treatments on the skin (impact on the epidermis and the dermis). Then, we studied publications dealing specifically with the skin of mummies obtained according to the various mummification processes. Whether this process of mummification is cultural (voluntary mummification) or natural (accidental mummification), it is in both cases a mechanism of desiccation leading to the complete elimination of water from the body and de facto the water from the skin. There is a total drying of skin that mainly made of collagen which is close, depending on the conditions in which the mummification process was carried out, to an extreme desiccation or freeze-drying. Thus, in the light of new technologies of molecular biology and imaging, this mummified skin reveals millennia-old secrets and has opened the field to a new discipline, paleodermatology. This discipline, which studies ancient skin, offers a singular scientific proof of the dermatoses of the time and the living conditions of the past.