Cosmetic creams may decrease the appearance of skin damage, including wrinkles, changes in skin pigmentation and surface appearance and feel. Cosmetic creams and lotions containing either copper peptide or vitamin C have biological function in the cells of the skin. The U.S. Food and Drug Administration does not regulate cosmetics except for ingredients that may pose a safety risk.

Vitamin C, also known as ascorbic acid, acts as an antioxidant when applied to the skin. According to MayoClinic.com, creams containing at least 10 percent vitamin C in the L-ascorbic acid form, with a pH of 2.5 or lower, improve the quality of collagen.

Copper is a mineral that is attached to peptides to promote absorption. According to "Dermatology Nursing," copper peptides enhance wound healing and copper is needed to make new collagen and elastin that support the dermis layer of the skin. According to a study reported In the October 2003 issue of "Journal of Drugs in Dermatology," copper peptides firm the skin through enzyme action and help to protect skin from free-radical damage.

The normal process of breakdown of ascorbic acid in solutions resulting in active and inactive metabolites. In the July 1994 issue of “Journal of the American Dietetic Association,” researchers point out that copper acts as an oxidant to increase the rate of breakdown to the inactive form, diketogulonic acid.

Ultraviolet rays and aging cause elastic tissue in the skin to break down, according to a study reported in the "Journal of Drugs in Dermatology". In addition, 1 percent of collagen in the skin is lost each year. Both vitamin C and copper peptides promote collagen production. To prevent interaction between copper peptides and vitamin C, MayoClinic.com recommends using them on alternate days. In addition, the authors point to a study showing copper peptides were more potent than vitamin C on improving collagen production.