Moisture, along with temperature and the mechanical factors previously mentioned, appears to be another key extrinsic factor in pressure ulcer development. The sources of skin moisture that may predispose the skin to breakdown include perspiration, urine, feces and fistula or wound drainage. Excessive moisture may lead to maceration . Reuler & Cooney theorized that one's risk of skin damage increases fivefold in the presence of moisture . Increases may be due to the slight increase in friction that occurs with light sweating or to the increase in bacterial load resulting when alkaline sources of moisture neutralize the protection provided by the normal acid mantle of the skin.

The detrimental effect of an increase in moisture adjacent to the skin has been demonstrated by tensile tests on excised skin strips in a controlled humidity environment. In Wildnauer's study, the tensile strength of the strips decreased 75% with an increase in relative humidity from 10% to 98% . Skin with such reduced strength may be more prone to mechanical damage from shear stress or abrasion.