 SCP-129 is a series of different species of fungus that can infect any animal with mucosal membranes. Infection by SCP-129 can pass through up to five stages, depending on exposure to further member species of SCP-129, individual resistance, and other factors, with each stage of infection facilitating progression to the next stage by weakening the individual's resistance to subsequent infection. Six of stage three infections are quite rare, but have the potential for widespread infection, if not swiftly isolated and contained. All known cases of SCP-129 have followed a five-stage progression, although data expunged, possibly due to mutation.