Human bacteria & pH.

Julie Le Bot

Skin Flora and its mysteries

      As surprising as it sounds, human body are not made only with human cells !

Indeed, according to some studies, there are as much no-human cells on our body as human ones. So obviously, organisms live in and on us. Even if these bacteria are part of ourselves, and most of them are not pathogens, some bacterial proliferation can involved infections and cause diseases to humans.

These organisms grow on different areas, according to parameters, as moisture, humidity, sun exposure or pH.The normal pH of human skin is around 5, and it is subject to change. Your environment, your diet or your lifestyle have an influence on it.

So if our pH skin can change, and pH has an influence on bacterial proliferation,  the followed question is : how pH actually impacts bacterial growth ?

Could we prevent ourselves from bacterial infections with a better care of our pH variation ?

Let’s try to find out the pH influence on bacterial -found on human skin - proliferation.

        To investigate on this question, the first step was to save some bacteria found on human skin. Superficial cells of human hands and fingers are the playground of thousands of microorganisms, which only waited for us to look at them. A sample of these finger microorganisms has been grown during two days in a 37°C incubator.

A study has shown that the pH skin could varies between 4.0 and 7.0. So to explore the influence of pH, four different media, at four different pH - 4, 6, 7 and 8 - have been prepared to host the finger bacteria, before let them grow during 12 hours at 37°C. 

                                     

      To measure bacterial proliferation, the number of colonies has been counted on every sample usable, after the incubation. Twenty three samples have been used, and final results show that neutral pH seems to increase the number of bacterial colonies. A very acidic (5) or basic (8) pH medium prevents bacteria to grow, and the more neutral it is, the more microorganisms reproduce themselves. Consequently, the normal pH of human skin doesn’t allow bacteria to grow, and protect human body. But with an unbalanced skin pH, an unusual bacterial proliferation can be expected.

       This short study shows even if the main part of living organisms which lived on our skin are no-pathogens, the pH of skin is also made to prevent from bacterial over-proliferation and protect us from diseases. The natural pH of human is balanced and individual -age and gender influenced it. To allow our skin to protect us, this pH has been maintain, by a lifestyle and an environment adapted. Still, this study is not precise enough to show clearly which pH variations are “acceptable”, without interfering with bacterial proliferation. The more precise information are on this topic, the more we can protect ourselves from infections. It is just a beginning !

If you want to know more about the fascinating world of human skin pH, let’s explore the articles cited on this post (find the list at the end) or look at the detail report of this experiment (https://docs.google.com/document/d/1oABJ0S5qxSTcHxBNB_NebG4SQxe_8jgZTuh453DresM/edit ) or the poster to illustrate it (https://docs.google.com/presentation/d/1KnFiFHuzUyDS4prCLgNIteTQ8XmPggL1b7vhFTF1QcE/edit#slide=id.g1727d17904_0_25)

Work cited :

Abbott, A. "Scientists bust the myth that our bodies have more bacteria than human cells." Nature. doi 10 (2016).

Price, Philip B. "The bacteriology of normal skin; a new quantitative test applied to a study of the bacterial flora and the disinfectant action of mechanical cleansing." The Journal of infectious diseases (1938): 301-318.

Lambers, H., et al. "Natural skin surface pH is on average below 5, which is beneficial for its resident flora." International journal of cosmetic science 28.5 (2006): 359-370.

Ehlers, C., et al. "Females have lower skin surface pH than men." Skin Research and Technology 7.2 (2001): 90-94.