This is a very vast area of research. One line of research can be; You can study the various types of cosmetics, with reference to their components and applications first. Then you can study their normal flora. Later you can study the types of organisms commonly existing in them and their effects on human body parts, where they are applied.
The newest application of biotechnology in the cosmetics is the regeneration of damaged skins and prevention of ageing, i mean biotechnology can make us living longer.Hair transplant as wayne rooney did is also another cosmetic application biotechnology. But your area of research is vague and you need to make it very specific.