After nine long months aboard the International Space Station, NASA’s astronauts have finally returned to Earth.
But Butch Wilmore and Suni Williams’ shockingly changed appearances have stunned the world since their landing on Tuesday.
In particular, their long stint in space appears to have turned the astronauts’ hair grey.
Williams, whose ‘gaunt’ appearance previously sparked health concerns, appeared notably different – with a long head of grey hair.
While some online commenters joked that this could be caused by a lack ‘of hair dye’ on the ISS, scientists say that space really can change your hair.
Research has shown that microgravity aboard the ISS interferes with hair growth.
Trapped outside Earth’s gravitational pull, hair follicles in astronauts’ heads start to undergo genetic changes that suppress growth.
Some studies even suggest that microgravity leads to an increase in ‘oxidative stress’ in hair cells, which is a potential cause of greying.
As the stranded NASA astronauts Suni Williams and Butch Wilmore return to Earth, their strikingly changed appearance has shocked the world
Suni Williams’ appearance stunned the world as she emerged from the SpaceX Crew Dragon capsule looking noticeably greyer
According to scientists, an extended period of time in microgravity can lead to reduced hair growth and increased levels of stress which could trigger greying. Pictured: Suni Williams being escorted on a stretcher after landing, March 18, 2025
Williams, 59, and Wilmore, 62, first arrived on the ISS in June aboard the Boeing Starliner spacecraft.
However, after a series of technical issues made it impossible to return on the problem-plagued capsule, the pair were forced to wait aboard the ISS until the departure of SpaceX’s Crew-9 mission in March.
In that time, Williams and Wilmore were exposed to the harsh conditions of space and the extreme stress of living in a floating laboratory 240 miles (386km) above the Earth’s surface.
Even during their stay, health experts were concerned that they may have been experiencing dramatic weight loss, but their return has raised new questions about the impact of space on the human body.
When Williams arrived on the ISS, her long flowing locks prompted Donald Trump to dub her the ‘woman with the wild hair’.
However, as Williams was helped from the SpaceX Crew Dragon capsule, following their splashdown of the coast of Florida, her hair appeared to have become grey.
On social media, commenters were quick to suggest that the change may be due to her grey roots growing out.
On X, formerly Twitter, one commenter wrote: ‘Well, looks like Suni Williams, stranded on the International Space Station, has run out of hair dye’.
Studies have shown that time spent in microgravity alters the genetic expression in human hair follicles, leading to reduced growth
On X, commenters attributed Williams’ change in appearance to a lack of hair dye which could have caused her grey roots to become visible
One commenter joked that Williams had ‘run out of hair dye’ during her time on the ISS
Another added: ‘She expected to be away for a week…so obviously she couldn’t continue coloring her hair.’
In reality, it is possible that Williams and Wilmore’s dramatic transformations are a product of the intense forces of space.
A study published in 2016 by scientists from the Japan Aerospace Exploration Agency (JAXA) found that microgravity alters gene expression in human hair follicles.
The study collected hair samples from ten astronauts living on the ISS for six months.
These samples showed that the spaceflight increased the activation of certain genes which restrict hair growth – prompting balding fears.
In the paper, Dr Masahiro Terada, a researcher at JAXA, wrote: ‘We found that spaceflight alters human hair follicle gene expression.
‘In some astronauts, genes related to hair growth such as FGF18, ANGPTL7 and COMP were upregulated during flight, suggesting that spaceflight inhibits cell proliferation in hair follicles.’
The study raises the prospect that humans may turn into a bald species if we start living in space and lose the ability to replenish hair as it falls out.
Williams’ changing appearance had sparked concerns earlier in the mission when pictures showed her looking ‘gaunt’
Studies show that microgravity causes changes in the genetic expression of human hair follicles. This activates more genes which suppress hair growth, particularly in men, which could lead to thinning or hair loss
The changes were also found to be more pronounced in male astronauts than in female astronauts.
Dr Terada wrote: ‘Although there are many differences such as hormone levels or functions between males and females, female astronauts appear to have a better response against the features of the space environment, as one example, FGF18 expression in females was more stable in space than in males.’
Likewise, a 2015 study looked at the skin and hair cells from mice who had spent three months aboard the ISS.
Researchers found that the mice had thinner skin and a disrupted hair follicle cycle.
Currently, there is no direct research into whether time spent in space causes hair greying.
However, there are studies which show spaceflight increases some of the known causes of greying.
In particular, studies have shown that changes to gene regulation during spaceflight leads to increased ‘oxidative stress’ in hair tissues.
Some research has suggested that oxidative stress, a type of damage created by harmful molecules called ‘reactive oxygen’, could be a key cause of greying.
There is no direct evidence to show that microgravity causes hair to turn grey. However, studies have shown that spaceflight causes extreme emotional stress which can take a serious toll on the body, including greying the hair
Having now returned to Earth, Williams (left) and Wilmore (right) will need to undergo a lengthy process of medical checks and a 45-day rehabilitation programme to recover
If spaceflight does increase oxidative stress in hair cells, this could explain why some astronauts’ hair appears to grey.
Likewise, astronauts undergo a huge amount of emotional stress during their time in space.
Studies have shown that astronauts undergo something called ‘long-term spaceflight composite stress’.
This is a combination of multiple sources of stress unique to space such as microgravity, isolation, confinement, constant noise, and circadian rhythm disturbance.
According to research from the China Astronaut Research and Training Center, this stress is so severe that it can even trigger depression and cognitive dysfunction.
There is well-documented evidence that experiencing stress causes hair to turn grey by triggering the body’s fight-or-flight reflex.
When this happens, your body’s nervous system releases a chemical called norepinephrine into the hair follicles which turns the hair grey or white.
Suni Williams’ transformation was so profound that it sparked a bizarre conspiracy theory claiming that the mission was faked and that she had dyed her hair before ‘returning’ to Earth. In reality, these confused conspiracy theorists had simply mixed up photos from before and after the mission, giving the impression that her hair had become darker
Although these conspiracy theorists did pick up on Williams and Wilmore’s changed appearance, they failed to realise which photos had been taken first
Given the stressful circumstances surrounding their stay on the ISS, it is perhaps unsurprising that Williams and Wilmore might look a little more grey once they finally got home.
Williams’ transformation was so profound that it sparked a bizarre conspiracy theory that the entire mission had been faked.
On social media, confused conspiracy theorists mixed up photos taken before and after the nine-month mission, taking this as evidence that Williams’s hair had actually darkened while in space.
One baffled commenter wrote: ‘It was nice that Sunita Williams thought to put a color through her hair to cover up the grey for the journey home.’
‘Not only that, but her gray hair magically transformed back to a rich, dark brown—no roots, no touch-ups, just pure space alchemy,’ another commenter mistakenly claimed.
EXPLAINED: THE $100 BILLION INTERNATIONAL SPACE STATION SITS 250 MILES ABOVE THE EARTH
The International Space Station (ISS) is a $100 billion (£80 billion) science and engineering laboratory that orbits 250 miles (400 km) above Earth.
It has been permanently staffed by rotating crews of astronauts and cosmonauts since November 2000.
Crews have come mainly from the US and Russia, but the Japanese space agency JAXA and European space agency ESA have also sent astronauts.
The International Space Station has been continuously occupied for more than 20 years and has been expended with multiple new modules added and upgrades to systems
Research conducted aboard the ISS often requires one or more of the unusual conditions present in low Earth orbit, such as low-gravity or oxygen.
ISS studies have investigated human research, space medicine, life sciences, physical sciences, astronomy and meteorology.
The US space agency, NASA, spends about $3 billion (£2.4 billion) a year on the space station program, with the remaining funding coming from international partners, including Europe, Russia and Japan.
So far 244 individuals from 19 countries have visited the station, and among them eight private citizens who spent up to $50 million for their visit.
There is an ongoing debate about the future of the station beyond 2025, when it is thought some of the original structure will reach ‘end of life’.
Russia, a major partner in the station, plans to launch its own orbital platform around then, with Axiom Space, a private firm, planning to send its own modules for purely commercial use to the station at the same time.
NASA, ESA, JAXA and the Canadian Space Agency (CSA) are working together to build a space station in orbit around the moon, and Russia and China are working on a similar project, that would also include a base on the surface.
