The author of the story kindly submitted here begins by writing, "I was Subject 26 in testing a living bacterial skin tonic, developed by AOBiome, a biotech sta

The author of the story kindly submitted here begins by writing, "I was Subject 26 in testing a living bacterial skin tonic, developed by AOBiome, a biotech start-up in Cambridge, Mass. The tonic looks, feels and tastes like water, but each spray bottle of AO+ Refreshing Cosmetic Mist contains billions of cultivated Nitrosomonas eutropha, an ammonia-oxidizing bacteria (AOB) that is most commonly found in dirt and untreated water. AOBiome scientists hypothesize that it once lived happily on us too — before we started washing it away with soap and shampoo." So what we are particularly talking about here is an early-phase human trial of a cosmetic product (which is regulated in the United States by the Food and Drug Administration under the Food, Drugs, and Cosmetics Act) which may or may not have the benefits claimed by the manufacturer. The trial is to find out if the new cosmetic does anything at all beneficial, without too much harm. Getting news coverage like this is of course public relations gold for the manufacturer. I read most of the comments here before reading the article and then posting my later comment. A lot of the comments revolve around the issue of the health effects of "modern" human life. All epidemiological evidence to date suggests that living like a middle-class or wealthier person from a developed country is good for health. An article in a series on Slate, "Why Are You Not Dead Yet? Life expectancy doubled in past 150 years. Here’s why."[1] refers to the steady long-term upward trend in healthy lifespan in the United States. Whatever we are doing about washing our bodies or our hair so far doesn't have any harmful effect that isn't swamped by the generally helpful effect of all the other changes of modern life. Life expectancy at age 40, at age 60, and at even higher ages is still rising throughout the developed countries of the world.[2] The overall trends are so favorable to further improvement to general health that if the observed facts about people who are already born and conservatively projected current trends continue, we can expect that girls born since 2000 in the developed world are more likely than not to reach the age of 100, with boys likely to enjoy lifespans almost as long. The article "The Biodemography of Human Ageing"[3] by James Vaupel, originally published in the journal Nature in 2010, is a good current reference on the subject. Vaupel is one of the leading scholars on the demography of aging and how to adjust for time trends in life expectancy. His striking finding is "Humans are living longer than ever before. In fact, newborn children in high-income countries can expect to live to more than 100 years. Starting in the mid-1800s, human longevity has increased dramatically and life expectancy is increasing by an average of six hours a day."[4] On evolutionary grounds, there is every reason to expect that human beings have haphazard adaptations through natural selection to survive to reproductive age despite a world full of microorganisms that were neither created nor evolved to benefit human beings, but rather just to survive and reproduce themselves. There is no evidence whatever that there are any large number of bacterial species or other microorganisms that are actively "beneficial" for human beings, rather than simply being well tolerated by human hosts. To live to healthy old age and greater enjoyment of the natural world and all its wonders, human beings may very well be better off continuing the human way of shaping their environments and culturally transmitting environmental interventions that lead to "unnaturally" good health and longevity. AFTER EDIT, TO RESPOND TO QUESTION BELOW: Yes, I am saying there is weak or no evidence of "beneficial" bacteria for human beings. This is to be expected from the consilient findings of evolutionary theory. (Human beings have had to live in highly microbe-free environments, for various reasons.) I am specifically asking for evidence, from medical review articles, that there are well accepted "beneficial" skin microbes. Which are they? What is the evidence that shows the benefit? The author of the article seems somewhat convinced by her personally experienced anecdote. It would of course take much more long-term study (not to mention more double-blind study designs) before we will be sure what is beneficial for human skin in particular and human health in general by way of applying bacteria intentionally to our skins. Suffice it to say that I am not afraid of washing my hands with soap nor afraid of washing my hair with shampoo. The book The Checklist Manifesto reports on an experimental study in a poor country of promoting hand-washing with soap, and how that showed evidence of improving health outcomes. Let's not throw out good hygiene with the bath water until more research has been completed on this interesting topic. [1] http://www.slate.com/articles/health_and_science/science_of_longevity/2013/09/life_expectancy_history_public_health_and_medical_advances_that_lead_to.html http://www.slate.com/articles/health_and_science/science_of_... [2] http://www.nature.com/scientificamerican/journal/v307/n3/box/scientificamerican0912-54_BX1.html http://www.nature.com/scientificamerican/journal/v307/n3/box... [3] http://www.demographic-challenge.com/files/downloads/2eb51e2860ef54d218ce5ce19abe6a59/dc_biodemography_of_human_ageing_nature_2010_vaupel.pdf http://www.demographic-challenge.com/files/downloads/2eb51e2... [4] http://www.prb.org/Journalists/Webcasts/2010/humanlongevity.aspx http://www.prb.org/Journalists/Webcasts/2010/humanlongevity....