Skin suits were disguises made of the skin of an individual.
The suits were used by several species. Among them were the Raxacoricofallapatorians and the Foamasis. If the skin was smaller than the individual using it, there were different techniques to use. The Raxacoricofallapatorians used compression field collars. Initially, the range of wearable skins were limited to humanoids of large builds and had the side effect of frequent gas expulsion. (TV: Aliens of London/World War Three) In the early 21st century, compression field technology later advanced to the point where they could fit inside the skins those of thinner frames and life forms the size of footballs. The gas exchange issue was fixed. (TV: The Lost Boy, PROSE: The Monsters Inside)
Raxacoricofallapatorians such as the Slitheen typically created skin suits from individuals they had murdered. Alternatively, synthetic skin suits were in use by 3764, when Slist Fayflut Marteveerthon Slitheen wore one based on an image of the Ninth Doctor broadcast from Fluren's World to act as the star of Doctor Who?. (COMIC: Doctormania)
The Foamasis were gifted with a biology that gave them hollow bones with double joints every few centimetres, a high liquid content, small organs and a retractable tail. (PROSE: Placebo Effect)