Two years after the spill, a study initiated by the National Institute for Occupational Safety and Health found biomarkers matching the oil from the spill in the bodies of cleanup workers. [citation needed] Other studies have reported a variety of mental health issues, skin problems, breathing issues, coughing, and headaches.[250] In 2013, during the three-day "Gulf of Mexico Oil Spill & Ecosystem Science Conference",[251] findings discussed included a '"significant percentage" of Gulf residents reporting mental health problems like anxiety, depression and PTSD. These studies also showed that the bodies of former spill cleanup workers carry biomarkers of "many chemicals contained in the oil".[252][253]