The external microbiome

The human is “not one landscape but many from the veritable desert of the arms and legs to the temperate woods of the scalp and the lush humid jungles of the armpit and groin.”

–        Mary J Marples ‘The Ecology of the Human Skin’

People are becoming increasingly more aware of the gut microbiome and the effects that this can have on diverse aspects of health, but there is less widespread knowledge of the skin microbiome. Just like the gut, the skin is also a complex eco system made up of a wide array of microorganisms such as bacteria, viruses, fungi and mites.

Many of the bacteria are the same as those found in the gut, but differ in their quantities. Actinobacteria, for example, tend to dominate on the skin, whereas Firmicutes and Bacteroidetes are found in larger numbers in the gut. Different areas of the body also host different types of microbes depending on the environment they offer i.e. dry, oily or moist. The forehead, armpit and hands all have their own communities of microbes, and microbes on the left hand can differ to those on the right.

We acquire our external microbiome the same way that we gain the ones in our gut; through the birth canal during labour. In fact, children born by caesarean section have a different set of skin bacteria to those born vaginally. Other factors affect the composition of our microbes such as environmental influences; our sex, age and occupation; clothing and cosmetics; and our use of antibiotics and antibacterial products.

The old belief was that all bacteria should be banished from our environment and bodies, yet the microbes on our skin are usually harmless and, in most cases, play a beneficial role. They help to provide a protective barrier which prevents the pathogenic bacteria from colonization. They can also help to modulate the immune system, clear up our dead skin cells, make moisturisers from oils secreted from our skin, and new research suggests they may even help prevent skin cancer.

Despite these benefits the skin microbiome can become dysbiotic, just like the eco system in the gut. Acne, athlete’s foot, ring worm, seborrheic dermatitis and eczema may all be signs that there’s an imbalance in the bacteria on the skin, and microbes that find their way to the wrong place can also cause harm. Bacteria that breach the skin barrier and get into wounds can cause inflammation and prevent healing. S. epidermidis is a harmless, commensal bacterium when found on the skin, yet it is also the most frequent cause of hospital acquired infection on devices such as catheters and heart valves.

We, in turn, can also cause our skin microbes harm. The personal care products we use often contain toxins that destroy the healthy symbiosis of our microbial communities; killing off beneficial bacteria and compromising the skin barrier. Even straightforward soap can alter the naturally slightly acidic PH of the skin and create a more alkaline environment that isn’t as favourable for the bacterial flora.

Antibacterial products such as hand sanitisers that contain the chemical triclosan are particularly damaging. In a study by researchers at Missouri University it was found that hand sanitizers increased the skin’s absorption of the hormone disrupting chemical BPA from till receipts. People who had used hand sanitizers before handling the till receipts had blood and urine levels 100 times higher than those who hadn’t.

So, how do we take care of our skin microbiome?

Use natural, toxin free cosmetics; go easy on the soaps and utilise essential oils instead of antibacterial chemicals. Essential oils can target pathogens but are more selective than conventional antibacterial agents, so don’t cause as much harm to the beneficial bacteria.

Many people use oral probiotics to support their gut bacteria, but now topical probiotics are becoming available to directly support skin health. Dermatologists are recognising the benefits of these and companies such as L’Oréal, Clinique and Estée Lauder are already formulating products containing probiotics.

A company called ‘Mother Dirt’ offers a range of products containing live ammonia-oxidising bacteria (AOB) in order to replace the ones that would have been naturally occurring on our skins before the advent of cleansing agents. AOB convert irritating components of our sweat (ammonia & urea) into byproducts that bring benefits to the skin (Nitrite and Nitric Oxide). Nitrite helps keep bad bacteria in check and Nitric Oxide is an antioxidant that helps calm and soothe the skin.

There was a great article in the New York Times by Julia Scott who tested a Mother Dirt product. Follow the link below to read about her experience.

If you need some help wading through the information out there about what is ‘good’ or ‘bad’ to put on your skin, then The Environmental Working Group may be able to help you. They’ve produced a cosmetics database called Skin Deep which rates a wide range of personal care products – giving each one a hazard score to guide you as to which are the most and least harmful. They also have the Healthy Living App which you can use to scan products to review their ratings. See the links below…

“Think Dirty” is a similar App which you can also use to scan cosmetics and personal care products.

Nina Mansell

Nutritional Therapist Dip CNM, mBANT, rCNHC


  1. Ali, S. and Yosipovitch, G. (2013). Skin pH: From Basic Science to Basic Skin Care. Acta Dermato Venereologica, 93(3), pp.261-267.
  2. Blaser, M. (2014). Missing microbes. London: Oneworld Publications.
  3. Grice, E. and Segre, J. (2011). The skin microbiome. Nature Reviews Microbiology, 9(4), pp.244-253.
  4. Guéniche, A., Bastien, P., Ovigne, J., Kermici, M., Courchay, G., Chevalier, V., Breton, L. and Castiel-Higounenc, I. (2009). Bifidobacterium longum lysate, a new ingredient for reactive skin. Experimental Dermatology, 19(8), pp.e1-e8.
  5. Hormann, A., vom Saal, F., Nagel, S., Stahlhut, R., Moyer, C., Ellersieck, M., Welshons, W., Toutain, P. and Taylor, J. (2014). Holding Thermal Receipt Paper and Eating Food after Using Hand Sanitizer Results in High Serum Bioactive and Urine Total Levels of Bisphenol A (BPA). PLoS ONE, 9(10), p.e110509.
  6. Knight, R. and Buhler, B. (2015). Follow your gut. New York: Ted Books, Simon & Schuster.
  7. Lambers, H., Piessens, S., Bloem, A., Pronk, H. and Finkel, P. (2006). Natural skin surface pH is on average below 5, which is beneficial for its resident flora. International Journal of Cosmetic Science, 28(5), pp.359-370.
  8. Marples, M. (1965). The Ecology of the human skin. Springfield (Ill.): Charles C. Thomas.

Share this page