# Seventy-one ISS astronauts logged 754 medical events, and 85 percent reported sinus or nasal problems while pseudoephedrine was used 95 times

> A stubborn medical mystery follows many astronauts into orbit: healthy crew members often develop blocked noses, facial puffiness and pressure around the ears soon after reaching space. For some, the discomfort fades as the body adjusts. Others continue reporting symptoms months into...

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Published: 2026-08-21T23:20:02+00:00
Categories: Explainer, Space

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A stubborn medical mystery follows many astronauts into orbit: healthy crew members often develop blocked noses, facial puffiness and pressure around the ears soon after reaching space. For some, the discomfort fades as the body adjusts. Others continue reporting symptoms months into a mission.

A 2025 [study](https://pmc.ncbi.nlm.nih.gov/articles/PMC12322577/) in **Laryngoscope Investigative Otolaryngology** examined medical records from 71 astronauts who served aboard the **International Space Station**. Researchers counted 754 events involving the nose, sinuses, throat, or related ear pressure. Sixty astronauts, about 85 percent of the group, had at least one recorded event.

General congestion appeared in the records of 53 astronauts, equal to 75 percent of the full group. The paper concluded that "Sinonasal symptoms are a prevalent medical concern among astronauts aboard the ISS." The findings connect many early complaints with fluid moving toward the head in weightlessness, while later cases may involve air quality, irritation, pressure changes, or other causes.

## NASA records reveal a common problem

The research team, led by Faraz Khan, used de-identified information requested from the **NASA Lifetime Surveillance of Astronaut Health** program. The records covered astronauts from Expedition 1 in 2000 through Expedition 62 in 2019, representing almost 34 combined years in orbit.

Researchers searched for reports involving congestion, facial pain, sneezing, nasal dryness, difficulty breathing and trouble clearing the ears. They also examined medication logs. NASA includes space-adaptation-related [nasal congestion](https://www.nasa.gov/reference/appendix-e-health-and-medical-care-technical-requirements/) and ear or sinus pressure injury among medical conditions that crews may face during spaceflight.

**Nasal congestion** dominated the results, with 597 logged instances. Symptoms specifically described as fluid-shift related appeared 67 times. Ear clearing problems and pressure injuries appeared 17 times, while sneezing was recorded 14 times. More serious conditions were uncommon. The data included one recorded case of sinusitis, four cases of rhinitis and five events involving infections in the ear, nose, or throat.

## Why fluids shift toward the head

Gravity pulls body fluids toward the legs when a person stands on Earth. In orbit, the body remains in continuous free fall, so fluids spread more evenly. Around two liters of fluid can leave the tissues of the lower body, with some moving toward the chest and head.

The resulting **headward fluid shift** can make an astronaut's face look puffy. Tissue inside the nose may swell, narrowing the passages used for breathing. Pressure can also build around the sinuses and ears, creating the familiar feeling of having a cold even when no infection is present.

A NASA [medical technical brief](https://www.nasa.gov/wp-content/uploads/2025/09/ochmo-mtb-004-space-adaptation-sickness-sas.pdf) describes facial swelling and head congestion as common early effects of **microgravity**. The kidneys begin removing extra fluid and the body gradually adjusts to its new environment. Symptoms linked to this first shift often ease within several days, although astronaut records show that nasal complaints can continue later in flight.

## The first week brings the most complaints

Of the 754 medical events studied, 713 included a specific flight day. The largest cluster occurred during the opening week, when researchers counted 107 events. Reports fell during the second week and generally remained at lower levels afterward.

The timing supports the fluid-shift explanation. An astronaut experiences the greatest physical adjustment soon after launch, when fluid moves upward and the body begins reducing its total fluid volume. The nose contains soft tissue rich in blood vessels, so even a modest change can restrict airflow and create a feeling of fullness.

Across all events with recorded dates, the average complaint occurred on flight day 70, while the median was day 61. An early surge can therefore exist alongside continuing problems. Some astronauts reported events beyond flight day 196, suggesting that several causes may contribute over the course of a long mission.

## Decongestants are common in orbit

Astronauts often treated the symptoms with medicines familiar to people on Earth. **Pseudoephedrine**, an oral decongestant, was recorded 95 times. **Oxymetazoline** nasal spray appeared 51 times. Congestion accounted for 184 medication uses, making it the leading reason for taking the drugs examined in the study.

Most uses were brief. The median recorded duration for pseudoephedrine and oxymetazoline was one day. A few courses lasted much longer, including 29 days for oxymetazoline. Extended use of such sprays can sometimes lead to rebound congestion, in which swelling returns after the medicine wears off.

The study did not measure how well the medications worked in orbit. Decongestants may reduce swollen tissue and provide relief, although they do not directly move fluid back toward the lower body. Researchers therefore raised the need to examine whether standard medicines offer the best long-term approach for congestion driven by spaceflight physiology.

## Spacewalkers logged more medical events

Spacewalks bring an added pressure challenge. The ISS operates at about 14.7 pounds per square inch, close to sea-level pressure on Earth. Spacesuits use lower pressures, about 4.3 psi in United States suits and 5.8 psi in Russian suits. Gas inside the middle ear expands as an astronaut moves into the lower-pressure environment.

If the passage connecting the middle ear to the throat becomes blocked, pressure may not equalize properly during repressurization. The result can be pain or **barotrauma**, a pressure-related injury involving the ear or sinus. Oxymetazoline and pseudoephedrine were sometimes taken before a spacewalk in an effort to keep these passages open.

Among the 60 astronauts with sinonasal events, 24 had records that mentioned **extravehicular activity**. They averaged 18.08 logged events, compared with 8.89 among astronauts whose records did not mention a spacewalk. The difference was 9.19 events on average. The study found an association rather than proof that spacewalks caused the extra complaints, since crews receive close medical attention before and after these demanding operations.

## Symptoms continue after early adaptation

Fluid movement provides a strong explanation for the first-week peak, yet it cannot fully explain every report later in a mission. NASA researchers have separately studied [ISS congestion](https://ntrs.nasa.gov/api/citations/20200001669/downloads/20200001669.pdf) after the opening week, when the initial fluid adjustment has largely settled.

The station is a closed environment where floating particles settle slowly. Material released during eating, shaving, or everyday work can remain in the cabin air and irritate the eyes or nose. Filters remove much of this material, although some exposure continues. The study found 12 irritation or hypersensitivity events and eight medication uses recorded for allergies.

Allergy medicines sometimes remained in use far longer than decongestant sprays. Loratadine had a maximum recorded duration of 340 days, while cetirizine reached 121 days. The records do not establish whether every long course treated a true allergy, since several antihistamines were listed under the broad indication of congestion.

## Limits in astronaut health records

The researchers carried out a **retrospective cohort study**, meaning they examined records that already existed. Such records reflect what astronauts chose to report and what medical teams entered into the system. Minor symptoms and self-directed medication use may have gone unrecorded.

The files also did not allow researchers to confirm the exact cause of each complaint. A blocked nose caused by fluid movement can feel similar to irritation, allergy, or an infection. Flight surgeons on Earth have limited ways to examine a patient hundreds of kilometers above the planet, even though NASA's [medical operations](https://www.nasa.gov/reference/medical-operations-and-clinical-care/) provide regular monitoring and trained support.

The spacewalk analysis relied on mentions of EVA activity within medication or medical notes. It did not use a complete list matching every symptom with a confirmed spacewalk date. Changes in reporting rules over the years may also have influenced the number of logged events, so the researchers avoided comparing one expedition directly with another.

## What Moon and Mars crews may face

Future crews may spend longer periods far from Earth and perform more work outside their vehicles. The planned **Artemis missions** will give researchers opportunities to study how nasal swelling and ear pressure behave beyond low Earth orbit. Mars expeditions would expose crews to microgravity for many months during each leg of the journey.

Possible countermeasures include methods that draw fluid toward the legs. Russian crews have used inflatable thigh cuffs, while other ISS research has tested lower-body negative pressure devices. Such equipment creates gentle suction around the lower body, encouraging blood and other fluids to move away from the head.

Better in-flight examination tools could also help doctors separate fluid-related swelling from allergies or infection. Standard symptom checks taken throughout a mission would reveal when complaints begin, how long they last and whether treatment provides relief. For astronauts with known nasal blockage before launch, carefully selected medical procedures may also reduce the amount of tissue that can swell.

The current evidence comes from a small and highly selected astronaut population, yet the high frequency of complaints makes congestion a practical issue for crew comfort and performance. Longer missions will require reliable ways to protect sleep, maintain clear breathing and help astronauts equalize ear pressure during repeated spacewalks.