Melanoma skin cancer is one of the most common forms of cancer contracted today. Although Ultraviolet B (UVB) radiation is known to cause the disease, little is understood of the effects of Ultraviolet A (UVA) radiation. John Simon of Duke University in the US has measured the absorption and emission of light from different sizes of natural and synthetic eumelanins - brown-black pigments on the surface of the skin - that are the main UVA receptors. He found that small particles of eumelanin (below 100 molecular weight) are more susceptible to absorbing UVA radiation than large particles.