A hand-held skin treatment device for applying light to skin of a subject to perform a treatment operation, the hand-held device comprising: a rigid main housing accommodating a cooling unit; a first treatment head portion coupled to the main housing for performing the treatment operation on a first skin portion, wherein the first treatment head portion comprises a first optical waveguide having a first skin-contact surface with a first total surface area, a first light source for generating light and applying the light to the first skin portion via the first optical waveguide and the first skin-contact surface, and a first heat sink thermally coupled to the first light source and to the cooling unit; a second treatment head portion for performing the treatment operation on a second skin portion adjacent to the first skin portion, wherein the second treatment head portion comprises a second optical waveguide having a second skin-contact surface with a second total surface area, a second light source for generating light and applying the light to the second skin portion via the second optical waveguide and the second skin-contact surface, and a second heat sink thermally coupled to the second light source; characterized in that the hand-held device is operable in (i) a first configuration in which the first and second treatment head portions (12; 20) are in a first spatial arrangement relative to the main housing such that, in an operational position of the main housing relative to the skin, only the first skin-contact surface is arranged in a treatment position relative to the main housing such as to be able to contact the skin over the first total surface area; and (ii) a second configuration in which the second treatment head portion is coupled to the main housing and the second heat sink is thermally coupled to the cooling unit, and in which the first and second treatment head portions (12; 20) are in a second spatial arrangement relative to the main housing, different from the first spatial arrangement, such that, in the operational position of the main housing, the first skin-contact surface and the second skin-contact surface are each arranged in a treatment position relative to the main housing such as to be able to contact the skin over, respectively, the first total surface area and the second total surface area. a rigid main housing accommodating a cooling unit; a first treatment head portion coupled to the main housing for performing the treatment operation on a first skin portion, wherein the first treatment head portion comprises a first optical waveguide having a first skin-contact surface with a first total surface area, a first light source for generating light and applying the light to the first skin portion via the first optical waveguide and the first skin-contact surface, and a first heat sink thermally coupled to the first light source and to the cooling unit; a second treatment head portion for performing the treatment operation on a second skin portion adjacent to the first skin portion, wherein the second treatment head portion comprises a second optical waveguide having a second skin-contact surface with a second total surface area, a second light source for generating light and applying the light to the second skin portion via the second optical waveguide and the second skin-contact surface, and a second heat sink thermally coupled to the second light source; characterized in that the hand-held device is operable in (i) a first configuration in which the first and second treatment head portions (12; 20) are in a first spatial arrangement relative to the main housing such that, in an operational position of the main housing relative to the skin, only the first skin-contact surface is arranged in a treatment position relative to the main housing such as to be able to contact the skin over the first total surface area; and (ii) a second configuration in which the second treatment head portion is coupled to the main housing and the second heat sink is thermally coupled to the cooling unit, and in which the first and second treatment head portions (12; 20) are in a second spatial arrangement relative to the main housing, different from the first spatial arrangement, such that, in the operational position of the main housing, the first skin-contact surface and the second skin-contact surface are each arranged in a treatment position relative to the main housing such as to be able to contact the skin over, respectively, the first total surface area and the second total surface area. (i) a first configuration in which the first and second treatment head portions (12; 20) are in a first spatial arrangement relative to the main housing such that, in an operational position of the main housing relative to the skin, only the first skin-contact surface is arranged in a treatment position relative to the main housing such as to be able to contact the skin over the first total surface area; and (ii) a second configuration in which the second treatment head portion is coupled to the main housing and the second heat sink is thermally coupled to the cooling unit, and in which the first and second treatment head portions (12; 20) are in a second spatial arrangement relative to the main housing, different from the first spatial arrangement, such that, in the operational position of the main housing, the first skin-contact surface and the second skin-contact surface are each arranged in a treatment position relative to the main housing such as to be able to contact the skin over, respectively, the first total surface area and the second total surface area.