The Oldest Treatment, Examined Anew
For more than two hundred years, the spa houses of Mariánské Lázně (Marienbad) have used the natural carbonic springs for therapeutic baths. Physicians of the 19th century already noticed the reddening of the skin and the sensation of warmth that a bath in water cooler than the body produces. Today these effects can be measured, and some of them are described in controlled studies.
The principle is simple: natural carbon dioxide dissolved in mineral water penetrates the body through the skin and acts mainly on the small vessels in the skin and subcutaneous tissue. This article summarises what is documented about carbonic baths, with references to specific studies and their limitations. It does not replace medical advice — the inclusion of baths in the treatment plan is decided by the spa physician at the initial examination.
How CO₂ Baths Work
Vasodilation and Skin Blood Flow
Carbon dioxide absorbed through the skin relaxes the smooth muscle of the small vessels. A review of CO₂ balneotherapy in cardiovascular disease summarises three main measurable effects of immersion in carbonic water: increased skin blood flow, a drop in body temperature and a sensation of warmth (Pagourelias et al., 2011, Int J Biometeorol).
How large the effect is was shown by a randomised crossover trial in 18 patients with arterial disease of the lower limbs: when the legs were immersed in carbonic water, laser-measured skin blood flow on the top of the foot rose by 300% and tissue oxygen partial pressure by 10%; in plain water of the same temperature, blood flow did not change. The increase persisted even after the legs were taken out of the bath (Hartmann et al., 1997, Angiology). The study used artificially carbonated water and measured a single bath — it is therefore evidence of the mechanism, not of a long-term result.
The increased oxygenation has a known explanation: a higher concentration of CO₂ in the tissue makes it easier for haemoglobin to release oxygen (the Bohr effect).
Arterial Disease of the Lower Limbs
The best-documented indication for carbonic baths is peripheral arterial disease of the lower limbs. In a randomised controlled trial in 24 patients with stable claudication, a four-week series of baths in carbonic water (five times a week, 30 minutes) increased both tissue oxygen and the distance patients could walk without pain; in the plain-water group the values did not change (Hartmann et al., 1997, Angiology). The sample was small and the water artificially carbonated.
A study of 46 people over 65 with risk factors for arterial disease points in a similar direction: after ten dry CO₂ baths, thermographically measured surface temperature rose in many regions of the body, consistent with better blood flow (Zbroja et al., 2021, IJERPH); the study had no control group. An older review concludes that controlled evidence exists precisely for arterial disease of the limbs, trophic ulcers, microangiopathy and mild hypertension (Resch and Just, 1994, Wien Med Wochenschr).
Blood Pressure
Dilation of the vessels lowers peripheral resistance, which is why carbonic baths are traditionally included for patients with hypertension. The evidence so far comes from smaller studies. In 35 spa patients in Bad Tatzmannsdorf, Austria, 24-hour blood pressure fell after three weeks of balneotherapy with carbonic and mud baths in people with medium and high baseline values; in people with low pressure it did not change (Ekmekcioglu et al., 2000, Altern Ther Health Med). The study had no control group and the baths were part of a broader programme.
In a randomised trial in 70 women aged 48–60 with climacteric syndrome, mean daytime systolic pressure fell by 13.7% and the menopausal index by 28% after ten dry CO₂ baths; the control group received no treatment (Chekhoeva et al., 2024, Bull Rehabil Med). These were dry baths in a specific group of women, so the result cannot simply be transferred to all patients with hypertension.
Carbonic baths complement the medical treatment of hypertension; they never replace it. A randomised trial in 84 patients with hypertension and obesity confirmed that a series of 15 baths had no adverse effect on metabolic or inflammatory indicators — balneotherapy is therefore not contraindicated in these patients (Oláh et al., 2011, Contemp Clin Trials). Hypertension of grade II to III is listed in the Czech indication list under code II/3; details can be found on the page indications and contraindications.
Wound Healing
Better blood flow and tissue oxygenation are also the reason CO₂ is used in the after-treatment of chronic wounds. A scoping review of 22 papers reports that CO₂ given in a bath, by injection or as gas on the skin improves local blood flow and oxygenation, dampens inflammation and, in the samples described, speeds the healing of chronic wounds on the limbs (Prazeres et al., 2025, Biomedicines). The strongest evidence comes from a double-blind randomised trial in 57 chronic diabetic wounds: after 20 applications of gaseous CO₂ to the skin, 20 of 30 wounds healed, and none in the control group treated with air (Macura et al., 2020, Int Wound J). This was gas applied to the skin, a procedure close to a dry gas bath, not a water bath; the sample was small.
What Makes the Springs of Mariánské Lázně Exceptional
Mariánské Lázně lies on volcanic bedrock from which natural carbon dioxide rises. Some 40 mineral springs rise in the town, naturally rich in CO₂, and alongside them the dry Maria's gas with a CO₂ content of 99.7%. It is the natural origin of the gas that distinguishes the carbonic baths here from the artificially carbonated baths used in some of the cited studies.
The carbonic baths in Mariánské Lázně use mineral water in which other dissolved substances combine with the carbon dioxide, above all bicarbonates, calcium, magnesium and iron. The composition of the individual springs can be found in the springs overview.
What a Typical Treatment Looks Like
A CO₂ bath in Mariánské Lázně usually lasts 20 minutes. The water temperature is kept at 33 to 34 °C — deliberately below body temperature, because CO₂ produces a sensation of warmth that makes the actual temperature seem higher. Fine gas bubbles form on the skin during the bath. The bath is followed by a period of rest lying down, which is part of the treatment.
The number of baths and their frequency are determined by the spa physician; they are usually prescribed as a series several times a week throughout the stay. The length of a covered stay is set by the item of the indication list with which you arrive — for hypertension of grade II to III (II/3), for example, the basic stay is 28 days in comprehensive care or 21 days in contributory care, for disease of the limb arteries (II/4) 21 days in both types of care. Self-paying guests choose the length in consultation with the spa physician.
What Is Documented and What Is the Aim
Summarised by strength of evidence:
- Skin blood flow and tissue oxygenation — measured in controlled studies, the effect sets in during the bath (Hartmann 1997).
- Arterial disease of the lower limbs — a small randomised trial showed longer pain-free walking after a four-week series (Hartmann 1997).
- Blood pressure — a fall in people with higher baseline values in a study without a control group (Ekmekcioglu 2000) and in one randomised trial of dry baths in women in the climacteric (Chekhoeva 2024).
- Healing of chronic wounds — reviews and one double-blind trial with gas applied to the skin (Prazeres 2025, Macura 2020).
- Quality of life in rehabilitation — in 149 women after breast surgery, quality of life and mood improved after three weeks of rehabilitation with CO₂ baths and peloids, most lastingly for fatigue; the study had no control group (Strauss‑Blasche et al., 2005, Cancer Nurs).
For the musculoskeletal system, skin diseases or states of exhaustion, carbonic baths are used on the basis of spa tradition as part of a broader programme drawn up by the spa physician.
Who CO₂ Baths Are Suitable For
In the Czech indication list, carbonic baths are among the basic treatments for diseases of the circulatory system (group II): hypertension of grade II to III (II/3), disease of the limb arteries (II/4) and functional disorders of the peripheral vessels and conditions after thrombosis (II/5). Depending on the patient's condition, the spa physician also includes them in programmes for other indication groups.
Contraindications include acute inflammation, uncompensated heart failure, recent thrombosis and certain skin diseases in the acute phase; the full list can be found on the page indications and contraindications. The inclusion of baths in the treatment plan is decided by the spa physician at the initial examination, in patients with hypertension in cooperation with their treating doctor.
Conclusion
The CO₂ baths of Mariánské Lázně combine a two-hundred-year tradition with a mechanism that can be measured today: carbon dioxide absorbed through the skin dilates the small vessels and increases blood flow and tissue oxygenation. Controlled studies document this for arterial disease of the lower limbs and for the healing of chronic wounds, smaller studies for blood pressure. For visitors who are looking for more than relaxation, carbonic baths are a treatment with a clearly described effect — and with a physician who decides whether and how to include it in their particular case.
