Nothing is better than a crisp, brand new George Washington bill that a vending machine gobbles up. And nothing is more frustrating than trying to flatten out an old, grimy, torn-up one dollar bill that a vending machine refuses to take. Thankfully, scientists have developed a new way to clean paper money and to prolong its life. The primary source of a banknote's aging and eventual yellowing is human sebum, the oily waxy substance the body produces. When the body makes just the right amount of human sebum, it protects the skin. Too little causes dry, cracked skin and too much terrorizes teenagers with acne problems. Not only does this sebum clog pores, but over time it builds up on the surface of dollar bills where it reacts with oxygen in the air and turns an aged yellow.