A cap to be placed on a head of a device for treating the skin of a user includes an inner part to be removably attached to the head of the device, an outer part to be placed against the skin of the user and an interior disposed between the inner and outer parts. A product is disposed in the interior for application to the skin of the user and a covering, such as a membrane which is disposed on the outer part or a sterilized pack, is removable before use. An assembly having the device and the cap is also provided.
