Small localized fat deposits and laxity of the body skin (knees, the inside part of the knee, abdomen, and arms) can be improved by using a fiber laser of 1470 nm. The single-use optical fiber (up to 400 microns thick) connected to the device is inserted under the skin in the area of fat localization and is moved “forward and backward” in a uniform manner in the entire area to be treated. The tip of the optical fiber emits energy (the wavelength of 1470 nm) that interacts with the fat and water. It causes lysis of adipose tissue (which will be reabsorbed) but, above all, heating of the water in the deepest layers of the dermis. The heating of the water will lead to the contraction of the tissues and improvement of laxity. The treatment is usually performed without anaesthesia and may require the use of air at -20°C (to cool the body surface) when are used fibres of the diameter not greater than 400 microns or equal. Large size fibers will require local anaesthesia. The session can be repeated after some months to improve the obtained effect.