Serine can be made in the tissue from glycine (or threonine) so it is nonessential, but its production requires adequate amounts of B3, B6, and folic acid. Serine is a constituent of brain proteins, including nerve coverings. It is also important in metabolism of purines and pyrimidines (part of the nucleic acids RNA and DNA), in the formation of cell membranes, and in creatine (part of muscle) synthesis. Serine has also been used as a natural moisturizer in skin creams. Serine is readily found in meats and dairy products, wheat gluten, peanuts, and soy products, many foods that can cause allergy. There is some concern that elevated serine levels (especially in sausage and lunch meats) can cause immune suppression and psychological symptoms, such as is seen in cerebral allergies.