Key Health Risks To Astronauts Traveling To The Moon

Here are three key health risks astronauts face in flying to the moon.

1. Radiation From Deep Space

Beyond Earth’s magnetic field and atmosphere, astronauts face galactic cosmic rays and solar energetic particles at much higher levels than on the ISS. This invisible hazard can increase lifetime cancer risk, damage DNA and potentially contribute to cardiovascular or neurological issues over time. A strong solar storm could deliver a higher acute dose.

For the short Artemis II mission, the risk is managed and comparable to about a month on the ISS, but it becomes more significant for longer stays or surface missions. NASA uses real-time monitoring, radiation sensors and is testing shielding technologies (like vests or storm shelters) to keep crews safe.

2. Lunar Dust Hazard

For this flyby, the crew stays inside Orion, but when astronauts start landing on the moon, that fine, jagged lunar soil becomes a serious concern. Apollo astronauts experienced “lunar hay fever” — irritated eyes, noses and lungs — after just a little dust snuck into the cabin. Studies show the sharp, reactive particles can inflame tissues and, in lab models, even damage lung and brain cells. Engineers are developing better filters, suit designs and habitat systems to limit dust exposure.

Harrison “Jack” Schmitt (Apollo 17), the only geologist to walk on the moon, experienced classic “lunar hay fever” — sneezing, nasal congestion, swollen nose, red/watery eyes and sore throat after dust entered the lunar module. Symptoms eased after a few hours, but he described it as an allergic-style reaction.

To address the serious health risks of lunar dust, NASA formed the Lunar Airborne Dust Toxicity Advisory Group, a dedicated task force of experts in toxicology, lunar geology and space medicine. Their studies on Apollo samples helped establish exposure standards and mitigation strategies that will protect future astronauts during extended stays on the lunar surface.

3. Microgravity And Partial-gravity Effects On The Body And Brain

In the weightlessness of deep space, the absence of gravity causes bodily fluids (blood and cerebrospinal fluid) to shift upward toward the head and upper body — a phenomenon called cephalad fluid shift. This redistribution increases pressure around the brain and eyes, triggering spaceflight-associated neuro-ocular syndrome, one of NASA’s top spaceflight-related health risks.

SANS includes a constellation of findings such as:

• Optic disc edema (swelling of the eye nerve)
• Posterior globe flattening (the back of the eyeball becomes compressed)
• Hyperopic refractive shift (a shift toward farsightedness, which can blur near vision)

Astronauts may notice headaches, visual disturbances or changes in visual acuity. While many cases on shorter missions are mild, structural changes visible on imaging (such as globe flattening or optic nerve sheath distention) can persist for years in some crew members. Studies show that roughly 70% of long-duration ISS astronauts experience some degree of these eye and brain changes, with severity generally increasing with mission length.

The exact cause is still being unraveled, but the primary driver appears to be the headward fluid shift leading to altered cerebrospinal fluid dynamics, possible mild elevations in intracranial pressure, impaired venous and lymphatic drainage and changes in the pressure gradient across the optic nerve. Other contributing factors under study include elevated cabin CO₂ levels, high-salt diets, intensive exercise regimens, variations in one-carbon metabolism (involving folate and B vitamins) and individual anatomical differences (such as a smaller optic cup volume). Inflammation and vascular changes may also play a role.

On the 10-day Artemis II mission, clinically significant SANS is less likely than on multi-month stays aboard the ISS. However, the crew is still collecting valuable data through in-flight vision testing, imaging and post-flight assessments.

NASA is actively addressing SANS with daily exercise protocols aboard Orion, wearable monitoring and broader research into countermeasures such as lower-body negative pressure devices, nutritional supplements, specialized eye protection or future artificial gravity concepts. The data gathered on this historic flight will help refine protections for longer lunar surface missions and eventual deep-space journeys.

Lessons From The Apollo Astronauts

Early data from the Apollo era continue to inform today’s preparations.

A landmark 2016 study found that the cardiovascular disease mortality rate among Apollo lunar astronauts was 43%, approximately four to five times higher than among non-flight astronauts (9%) or those who flew only in low-Earth orbit (11%). Some researchers have suggested this elevated rate could be linked to deep-space radiation exposure affecting the vascular endothelium, though the very small sample size (only seven deceased Apollo lunar astronauts in the primary analysis) means the findings remain debated and require further confirmation.

Several Apollo crews also experienced cardiac arrhythmias during flight (most notably on Apollo 15), along with the combined physical and mental demands of confinement far from Earth. These short missions were ultimately safe and successful, and the Artemis program builds directly on that knowledge with advanced real-time monitoring and countermeasures.

The beauty of this mission is that it’s not just about reaching the moon — it’s about doing it smarter and safer than ever before. NASA’s human research teams are turning every orbit into valuable science, gathering the knowledge we need to protect our astronauts while expanding humanity’s footprint across the solar system.

The Artemis II crew is writing the next chapter of human adventure, inspiring a generation to look up and dream bigger.