Why some long COVID symptoms eased after a month of guided spa treatment became clearer in a 2025 randomized controlled trial in BMC Complementary Medicine and Therapies. Researchers in Barcelona assigned 98 adults with post-COVID syndrome either to 12 sessions of balneotherapy plus aquatic exercise or to a control group, then tracked changes in pain, fatigue, sleep, mood, memory complaints, breathing limits and daily function.
The most striking gains came at treatment completion. The paper reports that the balneotherapy group improved more than the control group across several questionnaires, with the largest between-group changes in fatigue and pain. The authors also recorded 17 temporary symptom flares, usually early in treatment and often tied to fatigue or post-exertional malaise, which keeps the results grounded in the day-to-day reality of long COVID care.
Readers should keep the timing straight before treating the findings as durable. The first comparison came immediately after the treatment month, or one month after baseline for controls. A second comparison came at two months after baseline, which was about one month after treatment ended for the intervention group. Some advantages remained at that later point, yet several between-group differences had narrowed or disappeared, so the study supports cautious interest rather than a claim of lasting recovery.
What the Barcelona trial actually tested
The study was conducted at Hospital del Mar Research Institute in Barcelona and registered at ClinicalTrials.gov. Investigators randomized 51 participants to balneotherapy and aquatic exercise, while 47 stayed in the control group. Everyone had post-acute COVID syndrome, the broad cluster of symptoms that can persist well after the original infection and that has been described in major reviews such as the 2023 Lancet Commission paper on long COVID.
Balneotherapy in this trial meant more than sitting in warm water. Participants in the intervention arm attended 12 sessions across one month at a thermal spa facility. The program combined mineral-water immersion with supervised aquatic exercise. The design aimed to test whether a structured water-based program could reduce the symptom load that often keeps long COVID patients from working, exercising, or managing normal routines without relapse.
The researchers relied on a wide panel of standard questionnaires instead of a single headline score. They measured SF-36 health domains, sleep quality, anxiety, depression, memory failures, breathlessness, pain and post-COVID functional status. That wide lens makes sense because long COVID often affects many body systems at once, with overlapping physical and cognitive complaints that can reinforce each other.
Patients were followed at baseline, at the end of the treatment month and again at the two-month point from baseline. Four people in the balneotherapy arm dropped out, two because of fatigue and dizziness during the first sessions and two because of unrelated accidents. Four people in the control group did not answer follow-up questionnaires. Those details matter because completion is different from enrollment and follow-up is different again from the immediate post-treatment snapshot.
Where the clearest improvements appeared
The strongest signal was concentrated in symptoms many long COVID patients describe as the hardest to escape. According to the paper, the largest between-group changes after treatment were in the energy-fatigue and pain parts of the SF-36 questionnaire. The reported beta coefficients were large, the confidence intervals stayed away from zero and the p values were well below 0.0001 for both of those domains.
Several other measures also moved in favor of the water-therapy group at the end of the month. The researchers found significant between-group differences in emotional well-being, general health, perceived health change, post-COVID functional status, sleep quality, anxiety, depression, memory failures in everyday life and a visual analog pain scale. Taken together, those changes suggest that the intervention had effects across both physical discomfort and the mental strain that often rides along with persistent symptoms.
Even so, the paper does not say every symptom improved equally and it does not turn every numerical win into a lasting clinical promise. Breathlessness was measured with the modified Medical Research Council scale, yet the abstract and figures place more emphasis on fatigue, pain, sleep, function and emotional symptoms. The safest summary is simple: the broadest improvements appeared at treatment completion and the most prominent ones were in tiredness and pain.
The control group timing is important here. Control participants were compared after one month had passed without the spa program, which helps separate the intervention from ordinary short-term fluctuation. A randomized design gives this paper more weight than an uncontrolled pilot. At the same time, the outcomes still came from questionnaires, so the evidence is strongest for symptom experience, quality of life and function rather than for a biological cure measured in blood tests or scans.
Why the one-month follow-up changes the interpretation
Results looked less sweeping once the trial moved beyond the treatment month. At two months after baseline, roughly one month after the intervention had ended, some differences between groups were still present, especially for emotional well-being, pain, perceived health change and sleep quality. Several other outcomes no longer showed the same between-group separation they had shown immediately after treatment.
One-month follow-up is where the main caution lives. If a therapy produces a dramatic short-term reset that holds steady, the later comparison usually keeps most of the original pattern. Here, part of the pattern faded. The authors say that loss of some between-group differences leaves the long-term sustainability of the benefits uncertain, which is a careful reading of their own data rather than an afterthought tucked into the discussion.
Some fading at follow-up does not erase the earlier gains. Long COVID symptoms often rise and fall and a treatment that buys even a month of reduced pain or reduced exhaustion could still be meaningful for patients. What the follow-up does is narrow the claim. The study supports the idea that water-based treatment may relieve symptoms for a period of time; it does not show that 12 sessions reset the course of the illness for months afterward.
Another reason to avoid overstatement is that the study was powered around patient-reported outcomes, not around long-term relapse patterns. A larger trial with longer tracking could show whether booster sessions help, whether some subgroups keep more of the benefit, or whether the early symptom relief mainly reflects short-lived effects from warm water, exercise, structured attention, or temporary relief from everyday strain.
What the adverse-event record really says
The safety summary is encouraging, although it needs to be described with the same precision as the benefits. The authors report no severe adverse effects during balneotherapy. That line rules out a signal of major immediate harm in this trial, which matters when many long COVID patients worry about symptom crashes after physical activity or rehabilitation.
The absence of severe adverse effects sits alongside a second fact that belongs in every summary: 17 people reported mild and transient worsening of preexisting symptoms. The paper says these temporary flares were seen particularly in the first sessions and were mainly linked to fatigue or post-exertional malaise. For a long COVID audience, that is a familiar and important warning, because overdoing activity can leave some patients worse for hours or days even when no emergency develops.
Two intervention-group participants withdrew because of fatigue and dizziness during the first sessions. The trial flowchart also notes two other withdrawals in that group due to accidents unrelated to the intervention. Those details do not overturn the broader safety picture, yet they show that tolerability was uneven. A supervised pool program may still need slow pacing, close symptom monitoring and willingness to pause when early sessions stir up exhaustion.
The study therefore supports a more practical safety message than a simple declaration that the therapy was safe. Under clinical supervision, a month of thermal-water sessions did not produce severe adverse events in this small trial, yet temporary symptom worsening was common enough to deserve planning around. That means screening, pacing and follow-up are part of the intervention, not just paperwork around it.
Why water treatment could help and why that is still only part of the story
Process may be as important here as the mineral water itself. Warm immersion can unload joints, lower the effort needed to move and make gentle exercise easier for people whose bodies feel heavy or painful on land. Buoyancy can also help patients move through a larger range without the same impact. In a condition where pain and fatigue block activity, those mechanical changes are a plausible route to short-term relief.
Aquatic exercise adds a second layer. Instead of asking patients to push through land-based exertion, the program offered structured movement in a setting that can feel less punishing. Researchers cited earlier work suggesting that water-based rehabilitation may help with pain, mobility and mood in other conditions. The present trial is stronger than anecdote because of randomization, yet it still cannot fully separate the mineral-water environment from the exercise component built into the sessions.
The paper also sits within a wider scientific picture where long COVID remains complex. Reviews such as the Lancet Respiratory Medicine long COVID review in PMC describe overlapping problems involving inflammation, autonomic symptoms, sleep disruption, pain and impaired energy regulation. A therapy that improves several symptom clusters at once deserves attention. Complexity also means one helpful rehabilitation tool is unlikely to act as a universal answer for every patient.
Because the trial bundled several ingredients together, the mechanism stays partly unresolved. Mineral exposure, warm temperature, social support, expectation, therapist guidance and gentle exercise could each contribute something. That uncertainty does not weaken the symptom results already measured; it simply means the study shows that the whole package helped in the short term more clearly than it shows which single ingredient did the work.
What this trial changes and what it does not
The strongest reason to pay attention is that this was a randomized controlled trial in a field where many long COVID interventions still rest on small observational reports. Randomization helps the water-therapy arm stand out from ordinary variation better than a simple before-and-after design would. It also gives clinicians and patients a more serious data point when discussing rehabilitation options for people whose symptoms include pain, exhaustion, poor sleep and low mood.
A durable cure remains unproven, broad referral would be premature and the split between mineral-water immersion and carefully supervised exercise in warm water remains unresolved. Those gaps are exactly why the next trials need longer follow-up, clearer subgroup analysis and direct comparison against other paced rehabilitation programs.
For now, the headline remains specific and useful. In Barcelona, 98 adults entered a randomized study of 12 water-therapy sessions; the clearest benefits at treatment completion were reduced fatigue and reduced pain, while 17 temporary symptom flares reminded the researchers that symptom relief and symptom provocation can exist side by side. One month later, some advantages were still visible, some had faded and the evidence still pointed toward a promising but time-limited intervention.
That balance is what makes the paper worth reading carefully on PubMed as well as in the journal itself. The trial moves beyond vague wellness claims and offers structured evidence for a specific rehabilitation approach. Its own results also place firm boundaries around the claim: short-term improvement looks real, durability remains uncertain and careful pacing remains essential for a population that can worsen when effort exceeds what the body can handle.
