The concept of prebiotics is well known from food products, where several ingredients are used to stimulate the beneficial gut microflora. However, prebiotic substances can in principle be applied to balance almost any microbial community to achieve advantageous effects. Since many cosmetic products target skin bacteria as a cause for undesirable conditions like inflammation or body odour, prebiotic actives can help to cope with these problems in a very effective way. To ensure a focused and successful mode of action we demonstrated that it is essential to analyse the microflora and the interactions between different bacterial species carefully. These analyses were made using a molecular method, fluorescence in situ hybridization (FISH), allowing a precise determination of a bacterial community without the drawbacks of classical culture methods. In a further step it was then possible to identify new actives that inhibit harmful or unwanted bacterial species while protecting the beneficial flora. Using a quick and reliable in vitro screening method we found several plant extracts (e.g. Ginseng or Black currant) which inhibit the inflammation-causing bacterium Propionibacterium acnes, but do not affect beneficial species like coagulase-negative staphylococci. In addition, it could also be demonstrated that a prebiotic product line for treatment of inflamed (or acne prone) skin showed the predicted effects on the microflora composition in a first in vivo trial, i.e. decrease of Propionibacterium acnes at a constant level of total bacteria. After 3 weeks, the microflora of 91% of the volunteers had been rebalanced in this way. Furthermore, these formulations have been shown to exhibit excellent skin compatibility compared to an antibacterial product. Thus, prebiotic substances have the potential to provide a gentle and sustainable alternative to undirected antibacterial ingredients which can cause irritation, and frequently only show short time effects.

Paper presented at the IFSCC Conference 2005, Florence, Italy.