They're called "forever chemicals." Per- and polyfluoroalkyl substances, better known as PFAS, PFOS, and PFOA, are man-made chemicals that are all around us. It's expected that the average person has some exposure to the chemicals in their lifetimes whether it’s through food containers or the water we drink. The Environmental Protection Agency has linked exposure to certain levels of PFOA and PFOS to cancer, liver and immune deficiencies, as well as developmental effects to fetuses during pregnancy or breastfed infants. But as more information comes out about just how harmful these chemicals are, military firefighters--who had daily exposure to the chemicals in AFFF foam--are starting to wonder if it's the source of their myriad of mysterious health problems. "We used foam...we'd walk in and splash in it," said Mitch Gauge, a retired Senior Master Sergeant with the Delaware Air National Guard.