Process of cosmetic treatment of keratin materials, preferably skin or lips, comprises: applying to the keratin materials a composition (C2) comprising at least one active agent whose action on the keratin material can be triggered in response to an external stimulus； masking the localized zone to be treated and applying means able to make screen to the external stimulus on the adjacent surface of the localized zone； removing the mask of the localized zone； and exposing the keratin materials to external stimulus to bring the active agent to act on the localized zone to be treated. Process of cosmetic treatment of keratin materials, preferably skin or lips, comprises: applying to the keratin materials a composition (C2) comprising at least one active agent whose action on the keratin material can be triggered in response to an external stimulus, where the composition is applied on at least a localized area to be treated and on at least one surface adjacent to the localized zone； masking the localized zone to be treated and applying means able to make screen to the external stimulus on the adjacent surface of the localized zone； removing the mask of the localized zone； and exposing the keratin materials to external stimulus to bring the active agent to act on the localized zone to be treated. ACTIVITY : None given. MECHANISM OF ACTION : None given.
