Peanut skin is not only safe to eat, but a 2014 study published in Food Chemistry suggest that consuming the skin along with the peanut enhances its health, promoting nutritional value. According to the study, peanut skin is a rich source of phenolics, antioxidants and fiber that can prevent the onset of certain diseases and promote general wellness.
The study entitled, "Peanut-skin fortified peanut butter: effect of processing on phenolic content, fiber content and antioxidant activity," basically observed the effect of regular peanut butter and peanut butter that is fortified with peanut skins. Apart from being a good source of dietary fiber, the study also shows that peanut skin also contains bioactives.
Found mostly in plants, bioactives are substances that may have more health promoting benefits that is beyond what is offered by typical vitamins and minerals. The bioactives in peanut skin function as an antioxidant that can help protect against oxidative stress. This helps prevent the onset of certain degenerative medical conditions, such as heart disease, cancer and stroke.
Compared to the other parts of the peanut, the research also showed that the skin contains the most antioxidants. Roasted peanuts with the skin still intact also contain more phenolic compounds than blueberries.