Dave Witlock is a practical man. "I have not taken a shower in over 12 years," says the chemical engineer and Massachusetts Institute of Technology graduate. "No one did clinical trials on people taking showers every day. So what’s the basis for assuming that that is a healthy practice?"

Twice a day, Mr. Witlock applies a live bacteria solution of his own design to his skin. To spread the bacteria to everyone else, he has founded a company called AOBiome and is selling a spray that contains live ammonia oxidizing bacteria (AOB), called Mother Dirt.

From the Mother Dirt website:

Modernization of the Skin Microbiome

The main premise of AOBiome is that human skin was historically colonized with Nitrosomonas, a form of Ammonia-Oxidizing-Bacteria (AOB). AOB have evolved a specialized purpose: they derive their energy solely from consuming (oxidizing) ammonia and urea.

Why do we believe this? AOB are extremely ubiquitous in nature. This is because they play a crucial role in the nitrogen cycle everywhere on the planet. As a result, anywhere that we find ammonia (even if it is thousands of feet below sea level & has never seen daylight), we will find a form of Ammonia-Oxidizing-Bacteria.

But there is one exception: The only place that ammonia exists without AOB is human skin. This seems like an incredible outlier. Knowing how sensitive Nitrosomonas and other AOB are to modern soaps and detergents, we hypothesize that it was modern hygiene and the obsession with “clean” that has stripped us of this crucial microorganism.

The New York Times Sunday Review had an article this week linking autism with the hygiene hypothesis. Written by Moises Velasquez-Manoff, the piece is part of the Times' opinion coverage, not reported news. It was also one of those sort of stories that comes across as highly persuasive ... until you start looking at the details. About halfway through reading it yesterday, it occurred to me that Velasquez-Manoff was making a lot of big statements—"perhaps 1/3 of autism, and very likely more, looks like a type of inflammatory disease", for example—without citing the sources to back those statements up.

That's easy to do when you're writing a relatively short article summarizing the contents of a much bigger book, as Velasquez-Manoff seems to be doing here. But the problems go deeper than that, according to biologist and science writer Emily Willingham. In a must-read blog post, she goes through the NYT piece and points out many flaws in argument and detail. The main problem, though, is a pretty simple one: Moises Velasquez-Manoff presents what seems to be a largely speculative hypothesis as sure-fire truth. To make that case as persuasive as it is, he leaves out lots of evidence that doesn't match up with his thesis. Read the rest