Protein found in blood cells that, with the aid of enzymes, serves a vital function in the transfer of energy within cells. There are three types of cytochromes, indicated by A, B, or C, with cytochrome C being the most stable. However, because cytochromes require a complex process that is triggered by a sequence of other components to be effective in their function of cellular respiration, they serve no function alone when applied topically on skin.