A sealing element for a face seal assembly including a bellows portion having mounting portions at its axial ends. One of the mounting portions is designed for non-rotational mounting on a component, e.g. a shaft, and the other for retaining an annular face member. The sealing element is formed, on at least the faces thereof exposed to a medium to be sealed, from a plastics material selected from a group of plastics materials comprising PEEK and ECTFE. The sealing element serves for applying a bias force to the annular face member. The sealing element enables the design of an uncomplicated, easily maintained, externally pressurised single action face seal assembly which is particularly suitable for sealing aggressive media.