Abstract: We included seven randomised controlled trials with 891 participants (outpatients in secondary care). We found no quasi-randomised controlled trials. Six studies (836 participants) evaluated balneotherapy versus no treatment. One study evaluated balneotherapy versus a phlebotonic drug (melilotus officinalis) (55 participants). There was a lack of blinding of participants and investigators, imprecision and inconsistency, which downgraded the certainty of the evidence. For the balneotherapy versus no treatment comparison, there probably was no improvement in favour of balneotherapy in disease severity signs and symptom score as assessed using the Venous Clinical Severity Score (VCSS) (MD –1.66, 95% CI –4.14 to 0.83; 2 studies, 484 participants; moderate-certainty evidence). Balneotherapy probably resulted in a moderate improvement in HRQoL as assessed by the Chronic Venous Insufficiency Questionnaire 2 (CVIQ2) at three months (MD –9.38, 95% CI –18.18 to –0.57; 2 studies, 149 participants; moderate-certainty evidence), nine months (MD –10.46, 95% CI –11.81 to –9.11; 1 study; 55 participants; moderate-certainty evidence), and 12 months (MD –4.99, 95% CI –9.19 to –0.78; 2 studies, 455 participants; moderate-certainty evidence). There was no clear difference in HRQoL between balneotherapy and no treatment at six months (MD –1.64, 95% CI –9.18 to 5.89; 2 studies, 445 participants; moderate-certainty evidence). Balneotherapy probably slightly improved pain compared with no treatment (MD –1.23, 95% CI –1.33 to –1.13; 1 study; 390 participants; moderate-certainty evidence). There was no clear effect related to oedema between the two groups at 24 days (MD 43.28 mL, 95% CI –102.74 to 189.30; 2 studies, 153 participants; very-low certainty evidence). There probably was no improvement in favour of balneotherapy in the incidence of leg ulcers (OR 1.69, 95% CI 0.82 to 3.48; 2 studies, 449 participants; moderate-certainty evidence). There was probably a reduction in incidence of skin pigmentation changes in favour of balneotherapy at 12 months (pigmentation index: MD –3.59, 95% CI –4.02 to –3.16; 1 study; 59 participants; low-certainty evidence). The main complications reported included erysipelas (OR 2.58, 95% CI 0.65 to 10.22; 2 studies, 519 participants; moderate-certainty evidence), thromboembolic events (OR 0.35, 95% CI 0.09 to 1.42; 3 studies, 584 participants; moderate-certainty evidence) and palpitations (OR 0.33, 95% CI 0.01 to 8.52; 1 study; 59 participants; low-certainty evidence), with no clear evidence of an increase in reported adverse effects with balneotherapy. There were no serious adverse events reported in any of the studies. For the balneotherapy versus a phlebotonic drug (melilotus officinalis) comparison, we observed no clear difference in pain symptoms (OR 0.29, 95% CI 0.03 to 2.87; 1 study; 35 participants; very low-certainty evidence) and oedema (OR 0.21, 95% CI 0.02 to 2.27; 1 study; 35 participants; very low-certainty evidence). This single study did not report on the other outcomes of interest. We identified moderate- to low-certainty evidence that suggests that balneotherapy may result in a moderate improvement in pain, quality of life and skin pigmentation changes and has no clear effect on disease severity signs and symptoms score, adverse effects, leg ulcers and oedema when compared with no treatment. For future studies, measurements of outcomes such as disease severity sign and symptom score, quality of life, pain and oedema and choice of time points during follow-up must be standardised for adequate comparison between trials.

Plain-language summary: We identified seven randomised controlled trials (studies in which the participants were divided between treatment groups through random method) (most recent search August 2018). Six studies compared balneotherapy versus no treatment, and one study compared balneotherapy versus a medicine called melilotus officinalis. The studies used different types of balneotherapy and different treatment times. For the balneotherapy versus no treatment comparison there probably is no improvement in favour of balneotherapy in disease severity signs and symptoms score (moderate-certainty evidence). Balneotherapy probably improves health-related quality of life and pain (moderate-certainty evidence). There probably is no improvement in favour of balneotherapy for leg ulcers (moderate-certainty evidence). There is no clear effect related to oedema (swelling caused when fluid leaks out of the body's tiny blood vessels) between balneotherapy and no treatment (very low-certainty evidence). Balneotherapy probably reduces skin pigmentation changes (low-certainty evidence). None of the studies reported any serious adverse events. There were fewer side effects (infection and blood clots in the legs) in people receiving balneotherapy compared to no treatment. When comparing balneotherapy with melilotus officinalis, there were insufficient data to detect clear differences between the two treatments for pain and oedema in the single small study. There were no data available for the other outcomes of interest such as disease severity signs and symptoms score, quality of life, leg ulcers and skin pigmentation. The certainty of the evidence was affected by the small number of trials with few participants and the impossibility of blinding of participants and physicians conducting the balneotherapy treatment, which could have led to bias.