A device for light-based skin treatment is provided. The device comprises a light source for providing an incident light beam for treating a skin, optical elements for focusing the incident light beam in a focal point inside the skin, and a skin interface element for, during use of the device, providing optical coupling of the incident light beam from the device into the skin. The skin interface element comprises a transparent exit window for allowing the incident light beam to leave the device, on top of the exit window, a transparent mixture of a polar substance and an apolar substance, and on top of the transparent mixture, a transparent foil, the transparent foil being more hydrophobic than the exit window.