A chemical involved in immune system signalling may be able to reverse some types of skin damage caused by sunlight. It could reduce sunburn by activating DNA-repair mechanisms, suggests a new study by researchers from Germany-based University of Munster. This finding raises the possibility that the chemical might be used to prevent or treat skin cancer. The researchers found that IL-12 promotes repair rather than blocking ultraviolet rays, as most sunscreens do (www.nature.com, November 26, 2001).