A hand-held skin treatment device comprises a source of electromagnetic radiation, an energy supply electrically coupled to the source and a controller arranged to control the energy supplied to the source of electromagnetic radiation. The source, the energy supply and the controller are enclosed in a watertight housing allowing use of the hand-held skin treatment device in a wet environment. To provide sufficient cooling of the source, the device comprises an internal heat exchanger in heat conducting relation with the source, an external heat exchanger outside of the watertight housing, and a heat path from the internal heat exchanger to the external heat exchanger that passes hermetically through a wall of the watertight housing. With this device, users can conveniently integrate their skin treatment activities with the daily washing routine in a shower or bath. The device is especially useful in the context of hair removal.