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Without gravity, how do female astronauts menstruate while in space? —Gayle, Ventura, Calif.

For a while there, Gayle, the question wasn’t how women would menstruate in space but whether it was too risky to find out.

Although the first female cosmonaut, Valentina Tereshkova, had flown in Vostok 6 in 1963, women were excluded from the U.S. space program during its early years. The official reason for this was that, as a matter of policy, U.S. astronauts were drawn from the ranks of military test pilots, and all the test pilots were men. If you ask me, though, the real reason was American male panic about women and their mysterious inner workings. Several plane crashes in the 1930s had involved menstruating female pilots, and experts—male experts, of course—suggested that putting a woman with “menstrual disturbances” in the cockpit was an invitation to disaster. Eventually the more hysterical fears receded, but some space medics still harbored serious concerns about menstruation when NASA began planning to put women in space in the 1970s.

From a certain point of view, I suppose, these concerns weren’t completely crazy. When a woman has her period, normally the menstrual flow is forcibly expelled from the cervix. However, given the low-gravity environment of space, some scientists wondered about the possibility of “retrograde menstruation,” the backward flow of menstrual blood up into the fallopian tubes. This occurs sometimes on earth and is thought to lead to endometriosis, a disorder in which tissue that normally lines the uterus grows where it shouldn’t. Prior to the 1982 space shuttle flight by Sally Ride, the first U.S. woman to exit our atmosphere, consultants told NASA that female astronauts should take hormones to manage their menstrual cycles to reduce flow volume and ideally avoid having a period while in space.

Unsurprisingly, to women anyway, most of the anticipated problems never materialized. There’s no evidence retrograde menstruation occurs in space, and even if it did, it probably wouldn’t cause endometriosis: Reverse flow seems to trigger this condition only in those who experience it chronically. Returning women astronauts who’ve menstruated in space report that everything worked the way it usually does. The mechanics of a zero-G period haven’t been fully explicated in the scientific literature, but according to Principles of Clinical Medicine for Space Flight (2008), astronauts have “access to multiple sanitary products for menstruation, including pads, mini-pads, and tampons in plain and deodorant versions,” and presumably capillary attraction accomplishes what the lack of gravity can’t. (We might have predicted as much, since bedridden women usually menstruate OK.) Incidentally, for times when going to the bathroom is impossible for an extended period, such as launches, spacewalks, and landings, “crewmembers of both sexes have available a maximum absorbency garment (MAG) that can retain up to 2000 ml of urine, blood, or feces.” Not your ideal working conditions, but a small sacrifice to make for the world’s coolest job.

Female astronauts do face some challenges in space. Internal medicine specialist and space buff William Rowe notes that women are more likely to develop decompression sickness during their periods. That’s a problem mostly during space walks, so he suggests any excursion by a woman be timed for a different part of her cycle. Before you peg Rowe as a chauvinist scumbucket, note that he also thinks women are, on the whole, better suited than men to a low-gravity environment. In a 2004 article in the Journal of Men’s Health and Gender, he argues that for long-term space exploration an all-female crew might be the best bet. His reasons:

(1) Menstruation rids the body of iron. That’s a good thing, because space flight can reduce one’s production of a protein that normally sops up excess iron, and “increased free iron can be extremely toxic.”

(2) Women produce a lot more estrogen than men, and they also have lower epinephrine levels. For reasons we needn’t get into, these factors reduce the likelihood of heart attacks and other cardiovascular problems while in space.

(3) Some of the Apollo 15 astronauts experienced pain and swelling of their fingertips while on the surface of the moon. Rowe hypothesizes that this is less likely to happen to women because “estrogen reduces vascular smooth muscle tone.”

It might also be pointed out that women on average take up less room in cramped spacecraft cabins, consume fewer resources, and are more inclined to ask for directions when lost. Finally, to be blunt, who would you rather have up there: female astronauts who, worst case, are hormonally challenged on a fairly predictable schedule once a month, or male astronauts subject to random testosterone attacks any time at all? —Cecil Adams

Is there something you need to get straight? Take it up with Cecil on the Straight Dope message board, straightdope.com.