The skin is the most important barrier of the body providing protection against microbial infection, chemical or UV damage, dehydration and mechanical injuries. Repair of this organ after injury is thus a life saving priority. But how do skin cells know when to proliferate and at what rate? In the March 23, 2009 issue of the Journal of Cell Biology, Asst/P Tan Nguan Soon and colleagues reveal that skin fibroblasts use a protein called PPARβ/δ to make sure overlying epithelial cells don't proliferate too quickly. "Proliferation is important in early stages of wound healing," explains Tan. "But excessive proliferation isn't good: you can end up with hypertrophic scarring." Their results highlight how communications between different cell types are critical to maintain the skin as a barrier against the outside world.