A new report from the Institute of Medicine lists environmental factors that are linked to breast cancer, from X-rays to certain kinds of hormone-replacement therapy. The evidence is less certain for a many other exposures. Aruna Padmanabhan, an oncologist at Temple, says experts are fairly certain that consumer hair dyes, for instance, are no problem, but the research isn't definitive. "[T]here are many other factors that we can counsel our patients about, as in not using birth control pills if they have a high risk for breast cancer or losing weight, or increasing physical activity, these are things that we can guide our patients with," she said.