History was made on Oct. 18, 2019, when Flight Engineers Christina Koch and Jessica Meir of NASA finished the first all-female spacewalk. For roughly seven hours, the two women replaced a battery and performed a series of maintenance tasks on the orbiting lab. This landmark mission was technically supposed to have happened seven months earlier, but it was abruptly canceled due to the explanation that NASA didn't have two suits that fit.

Koch has been on board the space station March 14, doing scientific research as part of the Expedition 59 crew. She is scheduled to remain in orbit until February 2020; that mission will set a record for the longest spaceflight by a woman. The nearly year-long stay in space will also give scientists a chance to study the long-term effects of a spaceflight on women.

"Astronauts demonstrate amazing resilience and adaptability in response to long duration spaceflight exposure," said Jennifer Fogarty, chief scientist of the Human Research Program, in a NASA press release. "These opportunities have also demonstrated that there is a significant degree of variability in the responses of humans to spaceflight, and it is important to determine the acceptable degree of change for both men and women."

So far, the majority of research has been on men, most notably by former NASA astronaut Scott Kelly, who spent 340 days in space in 2015-2016.

We've been launching Earthlings into space for 58 years now, but only 11% of them have been women. In 1963, Soviet cosmonaut Valentina Tereshkova was the first woman in space. It took 20 years for NASA to follow suit, with Sally Ride becoming the first American woman in space in 1983. To give you an idea of how far we've come in gender-based stereotypes, NASA actually designed a makeup kit in 1978 — Ride opted not to use it.

The side effects of space

American, Japanese and Russian astronauts gather together for a picture on the ISS American, Japanese and Russian crew members gather for a group portrait in the Kibo laboratory of the International Space Station in April 2010. (Photo: NASA [public domain]/Wikimedia Commons)

When it comes to men, vision change is the biggest challenge when spending an extended amount of time in antigravity. Around half of the male astronauts who've journeyed to space have developed an intracranial pressure that reshapes their optic nerve and changes their eyesight. Women are not affected, and doctors are still at a loss to explain why.

However, women are more likely to feel sick going into space, while men are prone to re-entry sickness and diminished hearing when coming back to Earth. Doctors are also unsure if these are hormonal differences or physiological changes.

In an interview with the BBC, Dr. Varsha Jain, a space gynecologist for NASA, explained that menstruation and toilets are also an additional challenge for women — especially because engineers never factored in blood when building the International Space Station.

"In space, urine isn't wasted, it's recycled and drinking water is reclaimed from it," notes Jain. "Period blood is considered a solid material and none of the toilets on the space station can differentiate solid from liquid material, therefore the water in it is lost and not recycled." Jain adds that many female astronauts take a contraceptive pill or use an IUD to stop their period altogether.

Reproductive health is also a concern for both genders. Astronauts are at risk of radiation exposure while in space, but how that impacts their fertility is still unknown. "The quality of sperm and sperm count decreases after space travel, but then sperm regenerates back on Earth, so there is no known long-term damage," Jain says. "Women are born with all the eggs they need for their lifetime, so NASA is very supportive of female astronauts freezing their eggs before their missions."

Both male and female astronauts have successfully had children after completing a mission. But overall, Jain describes the physiological changes that happen to both men and women as an "accelerated aging process." Astronauts actually lose bone mass when they go into space, and much of it is never regained, despite the recovery countermeasures and programs in place back home.

As NASA continues to make sending humans to Mars their priority, more women should be launching into space to prepare for these future missions. Adds astronaut Koch: “Any time you increase the diversity of a pool of folks participating in any of those human research studies, you make the results of those studies more robust. We’re happy to be participating in those and to get the numbers up.”

Space affects women's and men's bodies in different ways
From nearsightedness to bone mass, a trip to the International Space System has a notable effect on astronauts' bodies.