An approach based on quantum and optical principles for changing the perception of skin tone has garnered a patent for physicists at The City College of New York. The method, devised by a team led by professor Robert R. Alfano, involves light-scattering nano- and microparticles being applied cosmetically to the skin to lessen the appearance of red, blue or yellow skin tones and to increase white tones. How someone perceives color is determined by how the item they are looking at scatters and emits light. For example, yellow skin appears that color because it scatters the yellow portion of the light spectrum (right, top). When a cosmetics preparation containing nano-/microparticles that scatter the blue portion of the spectrum is applied to the skin, it appears whiter because the scattered yellow and blue light mix (right, bottom). Courtesy of City College of New York. In August, three City College of New York physicists affiliated with the Institute for Ultrafast Spectroscopy and Lasers (IUSL) were awarded a patent for the method. IUSL director Alfano led the team, and research associate Xiaohui Ni played a key role in calculating the optical effects on nanometer-sized particles. The main application of the method, according to the patent abstract, will be to change the appearance of facial color from red, blue or yellow to white. Often, these hues are symptoms of medical conditions. For example, cyanosis – deprivation of oxygen to tissue near the skin – can cause skin to appear blue. Many people as they age develop rosacea, which causes skin to redden. The method can be applied to other products in which particles are applied to a surface or blended into a material, including paint and colored glass.