Chapter 8: Skin, Hooves and Nails

What do horses, guitarists and astronauts have in common? The question sounds more like the beginning of a joke told over a round of drinks than an important issue in space medicine. In fact, it’s a question that NASA flight surgeons asked when trying to solve the problem of spacewalker’s nails ― otherwise known as fingernail delamination, associated with repetitive finger stress working in a spacesuit.

Many astronauts use nail hardener to strengthen their nails, and anecdotal observations suggest that Hard as Hoof nail strengthening cream works well. The benefit of using topical equine products for humans is gaining popularity; in fact, some are convinced the best nail cream for brittle nails is Healthy Hoof cream, meant for horses. With hooves and fingernails both made from keratin, it is not a surprise that what works for a horse might help a human! If nothing else, it will make for an interesting conversation in the lunar habitat when one of the astronauts puts it on before a spacewalk.

Some feel that one of the benefits of space travel is that corns and calluses are no longer a bother in the absence of gravity. The characteristic hard, thick areas of skin can form anywhere on the body but occur most often in areas of frequent friction, irritation or pressure ― typically the weight-bearing part of the foot, or on the heel or toes if shoes are particularly tight. Floating around in a space station sounds like a perfect solution. No shoes are needed unless you’re running on the treadmill or cycling on the exercise bike. Otherwise, astronauts wear white socks. Sounds like blissful relief!

But calluses can form in space, though they are found on the top of the feet rather than the bottom or heel. While it is possible to float in a specific location in microgravity, for some tasks astronauts tuck their forefoot into restraining loops to stop themselves from floating away. Contact with the foot loop results in a point of friction on the top of the foot that over time may result in the formation of a callus.

Returning to Earth, astronauts find that the soles of their feet are smooth, while the tops are thick and callused like the soles were before the mission. This can be very uncomfortable when they start to wear shoes again, but over a couple of months the change in friction and weight-bearing shifts the areas of skin thickening back to the soles of their feet. Calluses can also build up on astronauts’ hands when they are in space. It’s easy for them to move about the space station by pulling themselves hand over hand, gliding gracefully between handholds, but using their hands so much for propulsion means that their skin thickens there instead of on their feet.