Green chemistry is a set of principles and guidelines that encourage chemists to design more efficient chemical processes, producing more of the chemical they want with less unwanted by-products. Most cosmetic ingredients are made using chemical processes to transform chemicals, including natural ingredients, into something more useful and safe when applied to the human body. The principles of green chemistry aim to ensure that chemists use less energy, less water and solvents, and fewer process steps (a smaller series of reactions).
We should note that green chemistry does not mean "no chemistry". Modern chemistry is essential for our modern lifestyle and all of the products we take for granted, from cars to consumer electronics and from clothing to cosmetics. However, green chemistry uses modern and innovative techniques so that chemistry is more efficient and less damaging to the environment.
For more information on green chemistry and its use in the making of cosmetic products you can visit the University of York Green Chemistry Centre of Excellence website to learn more.