Hydrotherapy and Circulation: What Actually Improves Blood Flow (and What Doesn’t)

Key Takeaways

• Just 5 minutes of warm water immersion at 40–41 °C increased femoral artery blood flow by 45.9 % and reduced leg vascular resistance by 29.1 % in a controlled study (Sasaki et al., 2021).
• Warm water triggers vasodilation through nitric oxide release — the same mechanism behind exercise-driven vascular health improvements.
• Percussive massage devices (massage guns) show some short-term improvements in muscle oxygenation, but the evidence base is still small and the effects are modest compared with water immersion.
• Cold water immersion at 5–10 °C for 10–15 minutes is the most effective protocol for post-exercise recovery, though its circulation benefits differ from warm water’s (Higgins et al., 2022).
• “Detoxification” through massage or hydrotherapy is not a medically supported concept — your liver and kidneys handle detoxification without assistance from massagers.

How Water Immersion Actually Affects Blood Flow

When you lower your body into warm water, several measurable physiological changes happen almost immediately. The hydrostatic pressure of the water compresses surface blood vessels, which pushes blood centrally. At the same time, warmth causes peripheral blood vessels to dilate — they widen — allowing more blood to flow through them.

A 2021 study published in Frontiers in Physiology measured these effects precisely. Ten healthy men (average age 44) were immersed in water at 40–41 °C for just five minutes. The results were striking:

• Femoral artery blood flow increased by 45.9 % (p = 0.002)
• Leg vascular resistance dropped by 29.1 % (p < 0.001)
• Aortic pulse wave velocity decreased by 7.5 % (indicating reduced arterial stiffness)

These changes occurred without any increase in core body temperature — meaning the vascular response was driven by the water itself, not by overheating.

The mechanism behind this is now well understood. Warm water increases shear stress on blood vessel walls, which triggers the endothelium (inner lining) to release nitric oxide. Nitric oxide relaxes the smooth muscle around arteries, widening them. This is the same pathway that regular aerobic exercise uses to improve long-term vascular health (Thomas et al., 2019).

Do Repeated Sessions Create Lasting Changes?

The acute effects of a single warm bath are real but temporary — blood flow returns to baseline within 30–60 minutes. The more important question is whether repeated exposure leads to lasting vascular adaptation.

An integrative review published in the International Journal of Environmental Research and Public Health (Thomas et al., 2019) examined the accumulated evidence. Key findings included:

• Repeated warm water immersion (36 sessions over 8 weeks at 40.5 °C) significantly improved flow-mediated dilation — a marker of how well arteries respond to increased blood flow
• The same protocol reduced carotid artery wall thickness by 8 weeks
• These improvements mirror some of the vascular benefits seen with regular exercise training

A large Japanese cohort study (Ukai et al., 2018, Scientific Reports) found that habitual hot water bathing was associated with better cardiovascular function in middle-aged and older adults compared with showering alone. However, this was observational — people who take regular baths may differ from non-bathers in other health-relevant ways.

Types of Hydrotherapy Devices: What the Evidence Supports

Not all “hydrotherapy massagers” are created equal. Here is an honest assessment of the main categories and what the research actually says about each.

Warm Water Foot Baths and Spas

Evidence strength: Moderate

Heated foot baths (typically 38–42 °C) cause local vasodilation in the feet and lower legs. A 2024 randomised controlled trial found that foot massage combined with warm water increased renal blood flow and activated parasympathetic nervous system responses in older adults (Suwannarat et al., 2024). These devices are inexpensive (£20–£80), accessible, and low-risk for most people.

Practical limitation: The blood flow increase is mainly local. A foot bath will not meaningfully improve circulation in your upper body or core.

Whirlpool and Jet Baths

Evidence strength: Moderate to good

Full-body whirlpool baths combine warm water immersion with mechanical pressure from water jets. A 2024 study on patients with peripheral artery disease found that whirlpool massage combined with supervised exercise improved peripheral circulation and physical performance (Mika et al., 2024). The combination of hydrostatic pressure, warmth, and massage likely provides additive effects.

Practical limitation: Most home hot tubs run at 37–40 °C, which is at the lower end of what studies have used. Professional hydrotherapy pools are typically better controlled.

Percussive Massage Devices (Massage Guns)

Evidence strength: Limited

Massage guns deliver rapid bursts of pressure to soft tissue. A systematic review in the Journal of Clinical Medicine (2023) analysed 13 studies with 255 participants and found modest short-term improvements in flexibility and perceived soreness. Some individual studies have shown increased local muscle oxygenation and skin temperature after 4–5 minutes of use.

However, the claim that massage guns “improve circulation” deserves qualification. As pain researcher Paul Ingraham has detailed, the circulatory effects of massage (of any type) are considerably smaller than commonly marketed. Your cardiovascular system pumps roughly 5 litres of blood per minute at rest — local massage cannot meaningfully change this systemic flow rate.

Practical limitation: Massage guns may temporarily increase local blood flow to treated areas, but there is no evidence they provide cardiovascular benefits comparable to warm water immersion or exercise.

Contrast Water Therapy (Hot/Cold Alternation)

Evidence strength: Moderate for recovery, mixed for circulation

Contrast therapy alternates between warm (38–42 °C) and cold (10–15 °C) water, causing blood vessels to repeatedly dilate and constrict. The theory is that this “pumping” action enhances circulation and clears metabolic waste.

A meta-analysis by Higgins et al. (2022) found that for post-exercise recovery, cold water immersion alone was actually more effective than contrast therapy for most outcomes including muscle soreness and perceived recovery. Contrast therapy showed some benefits over passive rest but wasn’t consistently superior to simpler methods.

Who Benefits Most from Hydrotherapy for Circulation?

Not everyone gets the same benefit. The evidence is strongest for these groups:

People with peripheral artery disease (PAD): Warm water therapy combined with supervised exercise has shown measurable improvements in peripheral circulation in this group (Mika et al., 2024). If you have PAD, discuss aquatic exercise with your vascular specialist.

Older adults: Age-related arterial stiffness responds to repeated warm water immersion, and the buoyancy of water makes aquatic exercise more accessible for people with joint problems.

People with hypertension: A mini-review by Goto et al. (2023) found that hydrotherapy and balneotherapy modalities generally reduced blood pressure, though study quality varied.

Athletes in recovery: Cold water immersion (10–15 minutes at 5–10 °C) after strenuous exercise reduces muscle soreness and improves perceived recovery, primarily through vasoconstriction-mediated reduction in inflammation rather than increased circulation (Higgins et al., 2022).

What Hydrotherapy Does Not Do for Circulation

Some common marketing claims about hydrotherapy massagers are not supported by evidence:

• “Detoxification” — Your liver and kidneys remove metabolic waste from your blood. No bath, massage, or device performs this function. Lymphatic drainage is a real physiological process, but it does not require commercial devices to function normally.
• “Holistic balance of body and mind” — Warm water feels pleasant and can reduce stress hormones (cortisol), but framing this as “balance” is marketing, not medicine.
• “Nutrient-rich blood to all organs” — Your circulatory system already delivers blood to all organs. The question is whether hydrotherapy improves delivery when it’s impaired — and for that, the evidence exists mainly in specific clinical populations (PAD, heart failure), not healthy individuals.

Practical Guidance: A Simple Home Protocol

Based on the research, here’s what an evidence-informed home hydrotherapy routine looks like:

For general vascular health:

1. Fill a bath to chest level at 38–41 °C (comfortably hot, not scalding)
2. Soak for 15–20 minutes, 3–5 times per week
3. Hydrate before and after — warm water causes sweating even when you don’t notice

For post-exercise recovery:

1. Cold water (10–15 °C) immersion for 10–15 minutes within 1 hour of exercise
2. Focus on the muscles you trained
3. This is most beneficial after high-intensity or eccentric exercise (running downhill, heavy lifting)

For foot and lower leg circulation:

1. A heated foot spa at 40 °C for 15–20 minutes
2. Particularly useful for people who stand or sit for long periods
3. Adding Epsom salt may contribute to relaxation but the magnesium absorption through skin is minimal

Safety Considerations

Warm water immersion is generally safe for most people, but certain groups should exercise caution:

• Heart failure or uncontrolled hypertension: Immersion increases venous return to the heart, which can be dangerous. Check with your cardiologist first.
• Peripheral neuropathy (e.g. from diabetes): Reduced sensation means you may not feel water that’s too hot. Always test temperature with a thermometer, not your skin.
• Pregnancy: Water temperatures above 38 °C should be avoided, particularly in the first trimester. Consult your midwife or obstetrician.
• Open wounds or active skin infections: Warm water can worsen infection. Wait until wounds are fully closed.
• Varicose veins: Heat can worsen venous pooling. Cool water or compression may be more appropriate.

The Bottom Line

Warm water immersion genuinely improves peripheral blood flow — and the effect is rapid, measurable, and backed by controlled studies. A regular bathing habit may produce lasting vascular benefits similar to (though smaller than) those from exercise.

However, many of the marketing claims around “hydrotherapy massagers” overstate what these devices do. A warm bath does more for your circulation than most expensive gadgets. If you have a specific circulation problem — peripheral artery disease, Raynaud’s phenomenon, diabetic foot complications — talk to your doctor about whether supervised aquatic therapy could help. For everyone else, the simplest intervention is also the most effective: get in warm water regularly, and stay active. Our equipment guide can help you choose the right setup.

Related Reading

• How Hydrotherapy Machines Actually Work: The Physics
• Hydrotherapy for Older Adults: Balance and Pain Relief
• Extreme Hydrotherapy Techniques for Fast Recovery
• Choosing the Right Hydrotherapy Equipment

References

• Sasaki, R. et al. (2021). Acute effects of short-term warm water immersion on arterial stiffness and central hemodynamics. Frontiers in Physiology, 12, 620201. PMC7890244
• Thomas, K.N. et al. (2019). The thermal effects of water immersion on health outcomes: an integrative review. International Journal of Environmental Research and Public Health, 16(7), 1280. PMC6479732
• Ukai, T. et al. (2018). Habitual hot water bathing protects cardiovascular function in middle-aged to elderly Japanese subjects. Scientific Reports, 8, 8687. Nature
• Goto, Y. et al. (2023). Effect of hydrotherapy, balneotherapy, and spa therapy on blood pressure: a mini-review. International Journal of Biometeorology, 67, 1529–1537. PubMed
• Mika, P. et al. (2024). Evaluation of peripheral circulatory changes following hydrotherapy and controlled physical training in patients with atherosclerotic lower limb ischemia. Life, 14(12), 1578. MDPI
• Suwannarat, P. et al. (2024). Immediate effects of Thai foot massage on renal blood flow and heart rate variability in community-dwelling older adults: a randomized controlled trial. BMC Complementary Medicine and Therapies. PubMed
• Higgins, T.R. et al. (2022). Impact of cold-water immersion compared with passive recovery following a single bout of strenuous exercise. Sports Medicine, 52, 1667–1688. PMC9213381
• Konrad, A. et al. (2023). The effects of massage guns on performance and recovery: a systematic review. Journal of Clinical Medicine, 12(19), 6329. PMC10532323