PFAS chemicals end up in our environment through the plastic products and other trash we throw out.

There is evidence that per- and polyfluoroalkyl substances can cause damage to the body. A review of the evidence in both rodents and humans shows that exposure to PFAS can contribute to a chronic condition that has become more common.

Synthetic chemicals are used in manufacturing plastic products. Because they don't break down easily, they end up being the grim nickname of forever chemicals. Many people and wildlife have levels of PFAS in their bodies at any given time.

These chemicals are not harmless. They mimic or otherwise disturb the body's hormones, which may raise the risk of various health problems, including cancer and infertility. According to the new research published Wednesday in Environmental Health Perspectives, the liver isn't spared from the effects of PFAS.

The data from over 100 studies that involved either rodents or humans was looked at by the researchers. They found a link between higher levels of PFAS in the body and higher levels of ALT. It's a worrying connection because high ALT levels in the blood are a common sign of liver damage.

Sarah Rock, a PhD student in the department of population and public health sciences at USC, is the lead author of the review.

In animals, Rock and her team found a link between exposure to PFAS and a disease called non-alcoholic fatty liver disease (NAFLD), which is not caused by chronic drinking. People can experience fatigue and abdominal pain, but NAFLD causes no symptoms of its own. The build up of fat can cause a condition called nonalcoholic steatohepatitis. People with NASH are more likely to develop serious problems such as permanent scarring, internal bleeding, and complete liver failure.

In the U.S., a quarter of adults are estimated to have it, along with rates of important risk factors for NAFLD such as obesity and type 2 diabetes. The authors say that it has been hard to study NAFLD and that the latest findings might show that chronic exposure to PFAS has had some role in this increase. There has been little research done on whether or not PFAS could be a contributing factor. Other studies have found a link between high blood cholesterol and PFAS, as well as higher levels of ALT in people, which can be a sign of fatty liver disease.

One limitation in studying the negative health effects of PFAS chemicals in general is that there are many such chemicals out there, and people are exposed to them in many different ways. It is difficult to tease out which ones are harming us and how they are getting into our bodies. In this review, the team isolated three different types of perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS) and perfluorononanoic acid (PFNA) as being associated with signs of liver damage.

The researchers say that more studies are needed to understand the complex nature of the exposure. They say that their findings show that these chemicals are a potential health threat and that more needs to be done about them.

Evidence from this study on liver injury, along with the work of many other researchers, suggest that we should be doing more to not only phase out PFAS use and but also actively remove it from our environment.