An anonymous reader writes "A biotech start-up from Massachusetts has an unusual product: a bottle full of bacteria you're supposed to spray onto your face. The bacteria is Nitrosomonas eutropha, and it's generally harmless. Its main use is that it oxidizes ammonia, and the start-up's researchers suspect it used to commonly live on human skin before we began washing it away with soaps and other cleaners. Such bacteria are an area of heavy research in biology right now. Scientists know that the gut microbiome is important to proper digestion, and they're trying to figure out if an external microbiome can be similarly beneficial to skin. A journalist for the NY Times volunteered to test the product, which involved four straight weeks of no showers, no soap, no shampoo, and no deodorant. The sprayed-on bacteria quickly colonized her skin, along with other known types of bacteria — and hundreds of unknown (but apparently harmless) strains. She reported improvements to her skin and complexion, and described how the bacteria worked to curtail (but not eliminate) the body odor caused by not washing. At the end of the experiment, all of the N. eutropha vanished within three showers."