Moises Velasquez-Manoff — a journalist and also, as it happens, a patient — has fallen hard for an idea known as the hygiene hypothesis, whose implications, if followed out along a widely branching chain of extended supposition, threaten to unravel much of what we think we know about health and disease.
This hypothesis argues that our modern obsession with eradicating germs has backfired into an explosion of disease, specifically all the “new” diseases that have replaced infections to undermine our health. The modern immune system, the idea holds, is stymied by the sudden absence of its customary microbial targets. With nothing constructive to do, it is crazily spinning its wheels, resulting in soaring rates of food allergies and asthma, arthritis, psoriasis, multiple sclerosis and diabetes, even heart disease and cancer — not to mention alopecia, the premature baldness from which Mr. Velasquez-Manoff suffers and which led him to the subject in the first place. (In an opinion article in The New York Times last month, he suggested that an immune disorder might account for many cases of autism.)
Clearly, if true, the hygiene hypothesis is the single greatest medical story of our time, undercutting a century of putative progress. Is it true? Probably some of it is. But Mr. Velasquez-Manoff’s ambitious compendium of data and supposition — a great dense fruitcake of a book whose 680 endnotes, the author notes apologetically, refer to only a minority of the 10,000 studies he consulted — spins it all out in the most positive possible way with an energy, eloquence and desire to believe that is both breathtaking and a little scary.