Congestion and Sinonasal Illness in Outer Space: A Study on the International Space Station

ABSTRACT

Objectives

This study aims to characterize quantitative data pertaining to sinonasal symptoms and their related medication use aboard the International Space Station (ISS). A secondary focus involves correlating these findings with mission parameters such as extravehicular activity (EVA) participation and mission duration.

Methods

This retrospective cohort study was conducted utilizing data requested from the National Aeronautics and Space Administration (NASA) Lifetime Surveillance of Astronaut Health (LSAH) program.

Results

Of 71 de‐identified ISS astronauts beginning with Expedition 1 in the year 2000 through 62 in 2019, there were 754 logged medical events; 60 astronauts reported any type of sinonasal medical event (85%), the most common being general nasal congestion in 53 astronauts (75%). Symptoms were attributed to microgravity‐induced fluid shifts in 34 astronauts (57%) while 17 (28%) attributed symptoms to ear clearing and barotrauma. Pseudoephedrine was the most used medication, with 95 recorded uses, followed by oxymetazoline spray at 51. Among the 60 astronauts with sinonasal medical events, the 24 with references to extravehicular activity (EVA) participation in their records had on average, 9.19 more records than those without (95% CI: 2.29–17.06).

Conclusion

Sinonasal symptoms are a prevalent medical concern among astronauts aboard the ISS. The findings suggest that early spaceflight‐associated fluid shifts contribute significantly to these symptoms, often requiring medication use. A correlation between EVA participation and a higher number of medical events highlights an occupational risk factor.

Level of Evidence

3.

1. Introduction

Nasal congestion has been established as a common complaint faced by astronauts while adapting to their new microgravity environment [1]. Previous research has indicated that congestion and allergy symptoms may represent the most common indication for prolonged medication usage in U.S. crewmembers aboard the International Space Station (ISS) [2]. With the rise of commercial spaceflight and increased participation by civilians in this sector, we would like to emphasize the need to fully explore the relationship between otolaryngologic health and microgravity. This will have increasing importance as individuals with imperfect health, comorbidities, and other risk factors participate in space travel.

Fluid shifts have served as the prevailing theory behind sinonasal congestion in space as approximately 2 L of extravascular fluid is lost from the lower extremities, with some of this fluid redistributed cranially [3]. This upward shift of fluid ultimately leads to symptoms of “puffiness” and nasal congestion experienced by astronauts during their adaptation period [4]. One previous study has found that there is an increased odds ratio for developing mastoid effusions in long‐term spaceflight [5]. Stenger and Marcias later hypothesized that it was likely related to fluid shifts as cases of otitis media and sinusitis in space are rare [6, 7].

The upcoming Artemis missions and future deep‐space expeditions to Mars will require astronauts to endure prolonged exposure to microgravity and the challenges that come with it [8]. Sinonasal symptoms, such as nasal congestion if unaddressed, could lead to decreased sleep quality, resulting in fatigue, impaired decision‐making, and decreases in productivity [9]. Addressing this gap before embarking on these future missions is essential, and retrospective analysis of ISS data offers valuable insights into long‐term symptom trends and medication usage. The primary objective of this study is to characterize sinonasal symptom burden and its related medication usage aboard the ISS. A secondary focus involves correlating these findings with mission parameters such as extravehicular activity (EVA) participation. EVA refers to any activity performed by astronauts outside of a spacecraft, such as spacewalks and repairs.

2. Methods

The NASA Lifetime Surveillance of Astronaut Health (LSAH) and the Life Sciences Data Archive (LSDA) were utilized for this retrospective cohort study. The NASA LSAH Evidence Based Working Group (EBWG) approved a request pertaining to medical events, medication usage logs on sinus and sinonasal health complications in astronauts aboard the ISS. This study was granted a Not Human Subject Research (NHSR) determination by NASA IRB (eIRB STUDY00000701) due to the request for medical files that were non‐attributable.

Data from NASA was thus queried for medical events related to sinonasal congestion as well as fluid shifts from gravitational changes. The request to the LSAH team included sinusitis, facial pain, rhinorrhea, congestion, sneezing, dry nose, eustachian tube dysfunction, difficulty breathing, facial puffiness, and difficulty clearing ears. For medication‐related data, a request was made for medications found in a Freedom of Information Act (FOIA) document that indicated some of the medications onboard the ISS medical kit [10]. Specifically, data pertaining to oxymetazoline, pseudoephedrine, diphenhydramine, fexofenadine, loratadine, olopatadine, and cromolyn was requested for the purposes of this study.

Jupyter Notebook version 6.4.8 was utilized to analyze data using Python 3.9.12. Additional Python modules were used to organize and analyze data, such as pandas. Data pertaining to medical events was first recategorized. The proportion of cases was computed by assessing the number of first‐time cases of each symptom category.

For medication related data, indications for usage were again recategorized in Python to four main categories of allergy, congestion, prophylaxis, as well as other. The prophylaxis category was created for pre‐EVA prophylaxis. While overlapping items were consolidated into these categories for clarity, we preserved the original clinical intent as recorded by NASA medical personnel, trusting their assessment. Counts were obtained for medication indication, medication type, as well as a comparison between indication and drug type. Lastly, medication usage duration was analyzed using the logged start day and end day in the data files.

A separate analysis was conducted on astronauts that had any mention of EVA activity in the medication or medical report logs. This cohort was compared to those that did not have any mention of EVA activity. A Mann–Whitney U test was performed between both groups.

3. Results

Overall, our cohort of 71 astronauts represents 33.94 years of cumulative time from Expedition 1 in the year 2000 through Expedition 62 in 2019. For the time period analyzed, 108 EVAs were performed by crewmembers, and a total of 754 otolaryngologic symptoms were logged. Eleven of the 71 crewmembers did not report any medical events of interest. General characteristics of our cohort are summarized in Table 1.

TABLE 1.

General characteristics of the astronaut cohort reported by NASA LSAH.

Characteristics		% cohort
Crewmembers total	71	100%
Has any sinonasal medical event during study window
No	11	15%
Yes	60	85%
Age grouping
Age < 50	45	63%
Age > 50	26	37%
Sex
Female	16	23%
Male	55	77%
Previous space travel
No	24	34%
Yes	47	66%
Mission duration
< 150 days	15	21%
150–200 days	47	66%
> 200 days	9	13%
Total EVA	108

Medical symptoms are summarized in Table 2. The category of general nasal congestion had 597 instances in the dataset, followed by specific fluid shift related symptoms at 67 instances. Ear clearing and barotrauma had a count of 17, followed by sneezing at 14. Irritation/hypersensitivity, along with discharge and rhinorrhea, had 12 unique instances each. Conditions that appeared to only represent respiratory pathology had six instances. Diseases not otherwise specified or uncategorized had five instances, along with any infections related to ENT anatomical sites. Specific documented cases of rhinitis and dryness were found to have four cases each. Eustachian tube dysfunction, generalized upper respiratory symptoms, sinus pressure, and earaches had two unique cases each. Lastly, unique documented cases of sinusitis, fatigue, and dysphonia or hoarseness had 1 unique medical event each. The cumulative incidence of each specific medical event type has also been summarized in Table 2. Of note, 75% of our astronaut cohort had logged records for general nasal congestion. Additionally, 48% of our cohort had cases specifically logged as fluid shift related symptoms.

TABLE 2.

First time cases and proportion of total logged cases by symptom.

Symptom category	N	First time cases	Proportion with logged records
General nasal congestion	597	53	75%
Fluid shift symptoms	67	34	48%
Ear clearing and barotrauma	17	7	10%
Sneezing	14	7	10%
Discharge and rhinorrhea	12	6	8%
Irritation/hypersensitivity	12	10	14%
Respiratory conditions	6	1	1%
Disease not otherwise specified	5	2	3%
ENT infections	5	2	3%
Rhinitis	4	4	6%
Dryness	4	3	4%
Eustachian tube dysfunction	2	2	3%
General upper respiratory symptoms	2	1	1%
Sinus pressure	2	2	3%
Earache	2	2	3%
Sinusitis	1	1	1%
Fatigue	1	1	1%
Dysphonia/hoarseness	1	1	1%
All events of interest	754	60	85%

About 713 of the 754 medical events had specific flight days recorded. Of these events with logged days, the overall mean flight day of a medical complaint of interest was 70 with a median of 61 and a standard deviation of 53.74. A histogram of the sinonasal medical events per flight week has been included in Figure 1.

FIGURE 1.

Sinonasal medical event count by flight day grouping. This bar graph illustrates the number of recorded sinonasal medical events among astronauts aboard the International Space Station (ISS) across different flight day groups. The highest number of events occurred during the first week of spaceflight, followed by a decline in subsequent weeks. Events continue to occur throughout long‐duration missions but at lower frequencies.

Data pertaining to medication use was organized by medication type and by indication logged in the records provided. This has been summarized in Table 3. The most common otolaryngologic indication for medication usage was nasal congestion at 184 recorded uses, followed by prophylaxis for EVA at 47. Among prophylaxis for EVA, oxymetazoline was recorded as the most frequently used medication (n = 26), followed closely by pseudoephedrine (n = 20). Other or unspecified uses were logged six times, and allergic indications were recorded eight times.

TABLE 3.

Medication usage statistics.

Medication name	Indication				Total count	Mean duration (days)	SD (days)	Min (days)	Median (days)	Max (days)	IQR (days)
	Allergy	Congestion	Prophylaxis	Other
Sodium chloride solution	0	1	0	1	2	87.50	81.32	30	87.5	145	57.5
Mometasone	0	14	0	0	14	53.14	61.30	8	26.5	241	35.25
Loratadine	5	27	0	2	34	22.62	58.42	1	7.5	340	9
Cetirizine	0	14	0	1	15	13.67	30.03	1	7	121	9
Diphenhydramine	1	4	0	0	5	7.20	5.40	1	7	14	8
Fexofenadine	0	18	1	0	19	12.37	15.49	1	6	48	17
Guaifenesin and pseudoephedrine	0	2	0	0	2	6.00	1.41	5	6	7	1
Loratadine and pseudoephedrine	1	3	0	0	4	3.00	2.83	1	2	7	3
Oxymetazoline	0	25	26	0	51	2.65	4.28	1	1	29	2
Pseudoephedrine	0	73	20	2	95	3.56	4.25	1	1	27	6
Saline nasal no‐drip nasal gel	0	1	0	0	1	16.00	—	—	—	—	—
Olopatadine	1	0	0	0	1	32.00	—	—	—	—	—
Prednisone	0	1	0	0	1	5.00	—	—	—	—	—
Unknown medication	0	1	0	0	1	14.00	—	—	—	—	—

The analysis for the duration of medication use is also summarized in Table 3. It is of note that medication logs with insufficient data regarding start and end dates were excluded from this analysis. A one‐time use of a drug counts as 1 day regardless of dosing.

There was a notable association between having any mention of EVA participation within the records and the number of sinonasal medical events logged. On average, those in this EVA cohort had 18.08 sinonasal medical events logged versus 8.89 sinonasal medical events in the non‐EVA cohort. This reflects a mean difference of 9.19 (95% CI: 2.29–17.06). This analysis was conducted on the 60 astronauts with any of the sinonasal medical events of interest and excluded the 11 astronauts without any such data.

4. Discussion

Herein we present the first comprehensive study on all types of sinonasal medical events and related medication usage for astronauts. In line with expectations, many of the symptoms recorded were primarily related to nasal congestion along with other fluid shifts. These two categorizations made up the majority of all complaints logged. For classification purposes, we followed what was explicitly listed in records, but we are cognizant that fluid shifts are one of the main causes of sinonasal congestion. Despite focusing on sinonasal complaints, we also received significant data related to barotrauma and pressure‐related injuries. This was welcomed as the nasopharynx and middle ear can be thought of as a unified system, with injuries often impacting both anatomical regions. Further, we presented data pertaining to the specific medications astronauts have used to manage sinonasal symptoms and for how long they attempted continuous or regular dosing.

It is of note that the data presented within this study concerning congestion and fluid shifts corroborates previous literature and reports which indicate nasal congestion as a prevalent concern for astronaut health and for medication utilization [2, 7, 11]. Within our study, the proportion of astronauts with logged cases of congestion and fluid shifts were 75% and 48%, respectively. Congestion was also the most prevalent indication for medication usage (n = 184) in our dataset. This raises another profound question: are earth‐based medications for congestion and symptom relief effective in the microgravity environment? If current literature affirms that cranial fluid shifts are the primary etiology of spaceflight‐associated nasal congestion, we must ascertain whether existing treatment options are the best approach. One study by Blue et al. suggested that this concern may be intensified by how ground‐based flight surgeons cannot truly examine their patients, and the exact etiology may be falsely assumed such as congestion from air quality when it may truly be due to fluid shifts [12]. Decongestants, since they do not address the underlying cause of fluid shifts, may thus be rendered ineffective for long‐term treatment. This is not to say that these medications cannot still provide symptomatic relief, however, one must consider the possible risks associated with rebound congestion from reliance. Despite having a low mean duration of use, oxymetazoline still had a maximum logged duration of 29 days, indicating that rebound congestion remains a possibility that astronauts must be cognizant of. It must also be considered that common ailments such as congestion do not require consultation from flight surgeons to medicate when aboard the ISS [12]. Interestingly, inflatable thigh cuffs have been employed as a strategy to manage cranial fluid shift in astronauts in earlier expeditions. The device in question is owned and operated by Russian Medical Operations and is known as Braslet‐M [13]. By sequestering fluid to the lower extremities, a reduction in cranial venous insufficiency was observed by vascular ultrasound. Furthermore, there appeared to be a reduction in subjective nasal congestion for ISS expeditions and previous Soyuz missions [14, 15]. If sinonasal congestion continues to represent an impediment to astronaut function and well‐being, we propose that a balance must be reached between symptomatic improvement and treatment of the underlying etiology. To mitigate congestion related symptoms and enhance astronaut eligibility, certain pre‐flight interventions may be beneficial. We foresee potential in procedural strategies such as radiofrequency turbinate reduction to decrease expansile tissue volume. Current NASA standards further affirm that complicated sinonasal history such as enlarged turbinates or obstructions to nasal breathing are disqualifying “unless medically or surgically corrected with normal function restored”, supporting the use of such interventions [16]. Given the expansion of spaceflight to a broader population, we believe these options will be considered in the years to come for individuals with preexisting sinonasal conditions. Addressing such issues preemptively could help minimize the effect of cranial fluid shifts, which may otherwise worsen nasal obstruction and impact astronaut well‐being.

While discussing the role of fluid shifts, one must also mention the role allergic reactions may have played in the data presented. Allergic indications for medication use were noted (n = 8) while irritation or hypersensitivity presented 12 times for the 71 astronauts. Previous literature has identified that microgravity environments may increase exposure to allergens and particulate matter. The dispersion of large particulates (greater than 100 μm) is exacerbated by the microgravity environment, which leads to a decrease in sedimentation of these particles. The longer these remain in the air, the potential for ocular and nasopharyngeal irritation in astronauts increases [17]. While high‐efficiency particulate air (HEPA) filters are used on spacecraft, there is still buildup of particulate matter that can occur after daily activities such as eating or shaving [12]. The possibility of transmission of infection also increases from person to person through spittle via atmospheric routes, increasing the potential for sinusitis [17]. A case study by Crucian et al. identified a case of persistent rhinitis and skin rash in a crewmember who displayed no history of terrestrial allergy. This crewmember experienced eye itching and sneezing in the ISS spacecraft that was responsive to oral antihistamines, further suggesting that their response was allergic in nature [18]. The medications used for allergy relief aboard the ISS include loratadine, diphenhydramine, loratadine with pseudoephedrine, and olopatadine. Interestingly, within our dataset, many of the same antihistamine medications were also recorded as being used for “congestion” highlighting that this grouping may contain some cases of allergic reactions. There is evidence that symptoms related to allergic reactions represent chronic illnesses as antihistamines had increased maximum durations of use such as loratadine at 340 days and cetirizine at 121.

EVA presents its own challenges to astronaut health during spaceflight. When transitioning from station pressure (14.7 psi) to the lower pressures used in spacesuits—4.3 psi for US suits and 5.8 psi for Russian suits—gases in the middle ear undergo a two‐to threefold expansion [19]. Eustachian tube obstruction during re‐pressurization may occur when the pressure differential exceeds 1.49–1.75 psi, after which muscular action cannot be used to overcome the negative pressure in the middle ear [20]. Thus, increasing time for re‐pressurization allows more gradual correction and could be tailored for each individual astronaut. A temporary stop in pressurization would be implemented if the astronaut experiences ear fullness and held until the middle ear pressure is balanced [19]. Decongestants like oxymetazoline were often used for EVA prophylaxis. However, the efficacy is likely reduced in view of the pre‐existing cranial fluid shift. Lastly, it appears that the 100% oxygen required during the EVA may serve as a contributing factor to ear barotrauma and ear block. The partial pressure of nitrogen in the middle ear would decrease as a function of the duration of 100% oxygen use. Thus, return to breathing normal air as soon as feasible and allowing time for nitrogen concentration to increase prior to completing the re‐pressurization protocol would further lower the probability of barotrauma. Our analysis further suggests that astronauts participating in EVA activity experience more medical complaints throughout their mission. This is likely due in part to the increased scrutiny and monitoring of astronauts before and after EVA activity by ground crew [19]. Future planetary missions will also see a rise in the frequency of EVA as well as the current complications related to EVA barotrauma [21]. We thus propose an evaluation of the efficacy of oxymetazoline in serving as the current mainstay prophylactic treatment since previous studies have indicated that there is insufficient evidence to support its use for prophylaxis in barotrauma related to aviation. There is, however, evidence to support the use of oral pseudoephedrine in this regard [22].

Our study does not present any data related to the efficacy of medication use during spaceflight. Previous studies suggest medication use for congestion has a lower rate of subjective effectiveness than medications taken as stimulants for headaches and medications for rash/allergies [22]. It must also be noted that the records summarized within this article are not comprehensive and error‐free. There appears to be continued underreporting of medication usage despite the introduction of strict documentation requirements [12]. This has also led to the understanding that temporal trends in such data may not be helpful as updated requirements are thought to play a role in any perceived increases in medication usage. Thus, this study did not present any longitudinal trends between expeditions, and such data was also withheld as it could make the cohort identifiable. Logged medical complaints are also subject to irregularity since the data relies on crew member reports to ground‐based flight surgeons and staff. The analysis on barotrauma related incidents focused on comments related to EVA in the records obtained rather than confirmed reports and dates of EVA participation.

Future prospective studies will be paramount in further investigating the relationship between otolaryngologic health and spaceflight. These studies should incorporate standardized longitudinal assessments as well as diagnostic tools to help overcome limitations from retrospective analysis.

Our analysis of medical events by flight weeks in Figure 1 supports the fluid shift hypothesis, as the greatest number of logged events (n = 107) occurred in week 1, the initial adaptation period. This is followed by a substantial decrease in events after week 1, with the number dropping in week 2 and remaining low in subsequent weeks. While there is some fluctuation, the overall trend tapers over time. It is also of note that the persistence of sinonasal medical events within the records may indicate other etiology. Fluid shifts likely contribute to the initial level of cases; however, it appears that logged records continue well past the 196th flight day. One must also consider that only a subset of our cohort had mission durations of such a length. Our work further indicates that, despite being uncommon, more complicated sinonasal symptoms do occur among astronauts in the form of sinusitis, rhinitis, as well as infections of the ears, nose, and throat. The data collected indicated that the proportion of astronauts with logged cases of these conditions were 1%, 6%, and 3%, respectively. As previously discussed, rhinitis has been documented aboard the ISS presenting alongside a skin rash for an extended duration [18]. This contrasts with the role fluid shifts play. Figure 1, as previously described, indicated that sinonasal medical events continue to occur well into the latter stages of an astronaut's stay aboard the ISS. If adaptation truly does occur towards the beginning of an expedition, then it is conceivable that latter symptoms represent different or perhaps more problematic triggers.

Otolaryngologists have historically served a prominent role in numerous task forces, committees, and institutions pertaining to space medicine [23]. Building on this historical tie, we urge the otolaryngology community to continue championing health and well‐being in the future of space medicine.

5. Conclusion

Our study details the high incidence of sinonasal symptoms reported in long‐duration spaceflight. Nasal congestion attributed to microgravity‐induced fluid shifts continues to be a prevalent issue among astronauts. Current measures taken for treatment or prophylaxis may be inadequate in addressing the root cause of these medical events. Although less common, there is also evidence of more complicated sinonasal disease impacting astronauts.

Conflicts of Interest

Masayoshi Takashima is a consultant for Neurent Medical and Medtronic ENT. Omar G. Ahmed is a consultant for Aerin Medical and Medtronic ENT. The authors have no other funding, financial relationships, or conflicts of interest to disclose.

Khan F., Ansingkar K., Dongre R., et al., “Congestion and Sinonasal Illness in Outer Space: A Study on the International Space Station,” Laryngoscope Investigative Otolaryngology 10, no. 4 (2025): e70229, 10.1002/lio2.70229.