Approximately how many types of bacteria are living on our skin, and what do they do there?
Dr Hettwer: The advances in recent microbiome analysis techniques revealed a much higher bacterial diversity on the skin as can be detected by traditional culture-based methods. In our own studies on acne prone skin, we detected bacteria from six phyla, more than 80 families and not less than 500 different species. You can imagine that this is only a fraction of what can be found in normal skin. Furthermore, skin of different ethnicity and on different places of our planet might harbour even more different species.

All in all, the amount of microorganisms living on our skin pretty much resembles the total cell number of our skin cells. The function of the bacteria is to block niches where pathogenic bacteria might be able to settle. To achieve this, our body creates the best conditions to feed the “good” microorganisms to enable a first protective shield against unwanted intruders.

This emergence of research in the skin microbiome might been seen as following the recent success of the food industry in promoting the benefits of ‘good bacteria’ – are the two areas of research connected?
Dr Hettwer: We have to distinguish where the microorganisms are used. The food industry targets the inside of our body, mainly the gut. On the one hand, you can re-balance a disturbed microflora in adding beneficial bacteria (pro-biotic). On the other hand, you can try to change the nutritional environment of the habitat of the microorganisms to promote the growth of the wanted species (pre-biotic). By doing so, the food industry tries to change the ecosystem of the gut to stimulate a proper digestive function and also the immune system, as it is known that the gut is a very important organ for it.

Skin biology is not as well investigated in respect to the microflora. However, in today’s tidy world, microflora are on bad terms as we regularly use cleansing products which will reduce the number of bacteria on our skin every day. Other external factors also stress the skin microflora. As such, it can be an important approach to take care of the skin’s microbiota.

For many years, problems like acne were managed with antibiotics. In light of new views on ‘good bacteria’, is this approach now considered detrimental?
Dr Hettwer: Severe acne cannot be treated with cosmetic solutions but is a pathological skin condition which needs to be diagnosed by a dermatologist. Retinoid treatment and antibiotics, the most powerful anti-acne therapeutics, have the advantage that they can be used topically and systemically to cure especially severe cases. Today’s antibiotics are in most cases selective to the target phylum of the bacteria and do not create a “tabula rasa” condition on the corresponding area of use. Cosmetic solutions for acne prone skin can mimic the dermatological armoury to prevent an aggravation of a mild condition. As a healthy microbiota is important to prevent the growth of deleterious species, it is crucial to choose intelligent molecules which target a specific sub-population of bacteria, in case of oily skin predominantly Propionibacterium acnes.