A proposed law in San Francisco would require the city's nudists to cover public seats with a protective barrier before sitting down. Supervisor Scott Wiener, who introduced the bill, claims that sharing bus seats, cafe benches, and restaurant chairs with naked people is a threat to public health. It's a claim that's been repeated in city ordinances and even a Supreme Court case. Does public nudity really increase the spread of infectious diseases?
Not especially. Unlike most cities in the United States, San Francisco law has allowed public nudity for years so long as it is not "lewd" (i.e. directly connected to a sex act). Yet the city's department of public health has no published cases of a person who became sick from exposure to the neighborhood nudists. Whatever bodily microbes one of them might deposit on a seat pose no more of a health risk than those you might find in a public restroom or pick up by shaking hands with a stranger.
There isn't much reason to fear getting a sexually transmitted disease from naked sitters. These infections are most commonly the result of vigorous and prolonged exposure of a person's mucous membranes, the thinner and more permeable skin found in the mouth and on the genitals. If you happened to share a seat with an infected nudist, you'd be protected both by your clothes and by your epidermis, which serves as an effective barrier against pathogens all by itself.
Scabies can survive apart from a human body for a few days, and are known to be transmitted via shared bedding or other nonsexual pathways. Extended, skin-to-skin contact does pose a risk of infection, but the danger of picking up the disease from a seat—especially if you're wearing clothes yourself—is negligible.
Diseases like salmonella, E. coli, and hepatitis A, which can be transmitted through the fecal-oral route, might also seem like threats, but there's no reason to believe that public nudity would lead to a significant rise in infection rates. Most people are regularly exposed to fecal-oral pathogens from other sources, including computer keyboards and dollar bills. The immune system of a relatively healthy and hygienic person is generally able to survive exposure to these pathogens in small quantities, and, indeed, most people do so daily. It's not impossible that one of these illnesses (or any other) could be transmitted from a nudist in an urban environment, but such events would be very uncommon. Public-health experts say that increased nudity would not lead to an increase in infection rates.
Got a question about the day's news? Ask the Explainer.
Explainer thanks Philip Alcabes of the City University of New York, and Stephan Brenner and Patrick Wilson of Columbia University.