The impact of gut bacteria on a broad range of human health conditions has captured the imaginations of both scientists and the general public in recent years. The understanding that the gut microbiome, which is the mix of bacteria, viruses and other microorganisms living in our gut, has a profound effect not only on our immune system (1) but also on our mental health (2), has opened up new ways of thinking about medicine. It is now emerging that the microbiome of our skin may play a similarly important role in our skin’s health. Water-containing skin care products contain preservatives to prevent bacteria from growing in them. Therefore it is possible that these antibacterial chemicals may also affect the population of microorganisms that are normally resident on our skin. It turns out that the effect on our microbiome of the preservatives in skin care products has had little investigation. This means that preservatives that are applied to our skin every day could be subtly affecting the health of our skin in ways we still don’t understand. This is in addition to the potentially damaging effects of some preservatives commonly used in skin care, particularly the parabens, which we have written about here.
What is the role of our skin’s microbiome?
A broad range of microorganisms live on our skin, and for some time it has been known that they play a role in protecting the skin from invasion by harmful species. Scientists are beginning to gain insights into how our skin’s microbiome protects us. One species of resident bacteria, Staphylococcus epidermidis, was found to secrete an enzyme that prevented the colonisation of the nasal cavity by the human pathogen Staphylococcus aureus. The enzyme also made S. aureus more vulnerable to attack by the immune system (3).
In addition to their vital role in keeping pathogenic bacteria at bay, these resident microorganisms are important in educating our immune system. Specialised immune cells living in our skin rely on a complex signalling system, primed by resident microorganisms, to distinguish resident bacteria from pathogenic bacteria. It now seems that resident bacteria like Staphylococcus epidermidis cooperate with our immune system in other ways too, by enhancing skin cell survival and repair during an infection, and reducing the intensity of the inflammatory response in certain conditions (summarised in 4). This evidence of cooperation between our immune system and our microbiome has led some to speculate that these microorganisms have co-evolved with us, creating an interdependence between us and our skin's microbiome (4).
Certain bacterial species are dominant in most healthy skin, and the balance of these populations is frequently altered when skin is diseased. It is still not understood whether the altered microbiome is a cause or an effect of these skin conditons, but it is now considered that an altered microbiome could play a role in skin diseases as diverse as acne, psoriasis, eczema (atopic dermatitis), seborrheic dermatitis and rosacea (summarised in 5).
What is the evidence that preservatives in skin care products change the skin’s microbiome?
Only a handful of studies have been performed to examine the effect on resident microflora of preservative-containing skin care products. In one study, skin creams containing the commonly used preservatives parabens, 1,2-hexanediol and phenoxyethanol inhibited the growth of some species of normally resident bacteria, while use of phenoxyethanol-containing products caused a reduction in some bacterial populations, and enhanced the growth of others, thereby disrupting the balance of the bacterial population in the skin (6). In another study, when skin care products containing the preservatives triclosan, phenoxyethanol or parabens were applied, there was an immediate reduction in the number of bacteria sampled from the skin (7).
It seems clear that preservative-containing skin care has the potential to alter our skin’s microbiome. Whether it also increases our risk of developing various skin conditions is still not clear, but it is possible that susceptible individuals may be harmed by the continuous, long term use of preservative-containing skin care products.
Mokosh certified organic skin care products are free of preservatives
Most skin care is made by mixing oil with water, and stabilised by detergent-like molecules known as emulsifiers (we have written about the problems with emulsifiers here). The presence of water creates an environment that allows the growth of bacteria and fungi, and therefore a suitable preservative needs to be added so that it is safe to use on the skin. We chose to formulate our range differently - without water, and therefore without the need for preservatives, emulsifiers and other synthetic ingredients. In a water-free environment, these microorganisms cannot grow. Therefore, there is little chance that Mokosh skin care products will affect the beneficial bacteria living in the skin.
We believe that as we learn more about the role of our skin's microbiome, we will come to understand that it is worth protecting for the better health and resilience of our skin. In the same way that we would avoid the unnecessary consumption of antibiotics for the sake of our gut microbiome, preservative-free skin care has to be the best option for our skin.
REFERENCES
1. Shreiner, A.B, et al. (2015) The gut microbiome in health and in disease. Curr Opin Gastroenterol. 31(1): 69–75.
2. Malan-Muller, S. et al. (2017) The Gut Microbiome and Mental Health: Implications for Anxiety- and Trauma-Related Disorders. OMICS: A Journal of Integrative Biology.
3. Iwase, T. et al. (2010) Staphylococcus epidermidis Esp inhibits Staphylococcus aureus biofilm formation and nasal colonization. Nature. 465:346-9..
4. Grice, E. A. and Segre J.A. (2011) The skin microbiome. Nat Rev Microbiol. 9: 244–253.
6. Jeong, J.-J. and Kong-Hyun, K. (2015) Effects of Cosmetics and Their Preservatives on the Growth and Composition of Human Skin Microbiota Journal of the Society of Cosmetic Scientists of Korea 41:127-134.
7. Lalitha, Ch. and Prasad Rao, P.V.V. (2013) Impact of superficial blends on skin microbiota. International Journal of Current Pharmaceutical Research 5:61-65
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