Hydrotherapy is a naturopathic modality that involves the therapeutic use of water to restore, maintain, and regulate health. It is also known as water therapy, medical therapy, and hydrothermal therapy. 

The modality covers a broad range of therapeutic techniques which utilise water's physical properties (temperature and pressure) to stimulate or influence various body systems. Mineral or herbal treatments are sometimes administered with hydrotherapy treatments (1,2). The use of natural mineral waters, gases and peloids (mud) is a form of hydrotherapy known as balneotherapy (3).

Water is used internally or externally, in any form (water, ice, steam), although hydrotherapy is predominantly administered via external practices, either to the entire body or specific areas. Applications vary widely, depending on treatment goals, and are individualised to the patient's condition. Examples include steam baths, semi-submersions (like sitz baths), saunas, and hot and cold compresses, wraps and lavations, among others (Table 1) (4,5).

The significant effects of naturopathic hydrotherapy are due to its ability to stimulate the body's innate healing mechanisms, mainly through manipulating circulation. Water's thermal and mechanical properties can be utilised to improve circulation, facilitate the delivery of oxygen-rich and nutrient-rich blood to various organs and tissues, and remove metabolic waste and toxins (4,5). 

Thermal effects are elicited via heat (typically 35-40°), body temperature (32-34°C) or cold therapy (8-10°C) (6). Heat therapy is associated with vasodilatory and circulatory effects, which promote muscle relaxation and analgesia. Cold therapy is associated with vasoconstriction and pain-reducing effects (6). The application of hot and cold therapy stimulates the body's homeostatic mechanisms and has physiological effects on lymphatic, immune and neuroendocrine systems (4,5).

Hydrotherapy is used widely throughout Europe and North America, as an adjunct treatment for a broad range of conditions including arthritis, fibromyalgia, congestive heart failure, chronic obstructive pulmonary disease, stress and anxiety, sports recovery, and for the rehabilitation of patients with an acute injury (2,6,7).

Table 1. Common naturopathic hydrotherapy treatments (4,5,8,9,10,11,12)

Traditional Understanding

Hydrotherapy is an age-old practice with reports dating back to Hippocrates' time, around 500 BC.  It has been used widely in ancient cultures, including Greece, India, Egypt, Japan, and China.  Hydrotherapy, alone or in combination with other prescriptions, was used traditionally for various conditions such as rheumatism, fevers, joint pain, mood disorders, and headaches (13).

Hydrotherapy was rediscovered and popularised in Europe during the 18^th and 19^th centuries. Modern naturopathic hydrotherapy has its direct historical roots in Germany, where it was formulated and practised in the German Forest sanatoriums by Nature Cure pioneers. Father Sebastian Kneipp, a 19th-century Bavarian monk, is widely regarded as the father of modern hydrotherapy. Kneipp's use of alternating hot and cold water, called contrast hydrotherapy, is still used today (14).

Hydrotherapy spread to the United States from Europe in the mid-19th century, and today naturopathic hydrotherapy is common, if not central, to current naturopathic practice throughout North America and Europe. Naturopathic hydrotherapy is a clinical treatment tailored to address specific needs of the patient. It may be combined with other treatments, including herbal medicine, homeopathy, and nutrition, to enhance therapeutic outcomes (5).

Naturopathic hydrotherapy was first practised in Australia in the 1840s and was a core of naturopathic practice in Australia for over a century. However, since 2002 it has not been part of naturopathic education in Australia and hydrotherapy has not been retained as a modality in Australian naturopathic practice (4,5). 

Latest Research

Cardiovascular disease

A growing body of clinical evidence supports hydrotherapy as an adjunctive non-pharmacological treatment for cardiovascular disease (15). These benefits primarily result from the effects of water on venous return and cardiac output (mechanical effects) and vasodilation and toning of vascular endothelium (thermal effects) (16).

Contrast hydrotherapy and thermal sauna therapy have been shown to improve peripheral blood flow with long-term improvements in vascular function (17,18,19,20). Hydrotherapy and sauna therapy has been shown to reduce other risk factors of ischaemic heart disease, including total and low-density lipoprotein (LDL)-cholesterol concentrations (21) and triglycerides (22).

Clinical and observational studies have demonstrated positive effects of hydrotherapy (including sauna) in the treatment of hypertension (23,24), congestive heart failure (25,26,27,28,29) and vascular endothelial dysfunction in atherosclerosis (18).

In congestive heart failure, thermal bathing or sauna improves cardiac function (25,26), exercise tolerance in association with improvement in endothelial function (28) and overall quality of life (27).

Hydrotherapy may also have benefits for conditions associated with a poor cardiovascular function (e.g. dementia). Results of two extensive observational studies found risk reductions not only for sudden cardiac death (63%) but also for dementia (66%) and Alzheimer’s disease (65%), as a result of regular sauna (4-7 times per week) (30,31).

Exercise recovery

Cold water hydrotherapy is a popular intervention for exercise recovery. Cold may facilitate recovery from exercise by reducing intramuscular temperature and metabolism (32). It also reduces hypoxic stress, ROS generation and subsequent damage (33,34), induces vasoconstriction to limit oedema formation (32,35), and reduces the inflammatory response and associated damage and soreness (36).

Several studies demonstrate that cold water immersion (CWI) (<15°C) is associated with lower fatigue, improved physical recovery, and delayed muscle onset soreness (DOMS) compared with passive interventions involving rest or no intervention (37,38). 

Contrast water therapy (CWT) is seen as an alternative to CWI for reducing symptoms of muscle damage and associated DOMS, although its mechanisms of action remain unclear (39,40). Body exposure to alternating high and low temperatures is believed to accelerate blood circulation, facilitating metabolite elimination (41).

A recent meta-analysis found benefits for CWT and CWI for recovery in team sports 24-48 hours after exercise. However, results of studies remain ambiguous, and long-term benefits (beyond 48 hours) need to be investigated (42).

Musculoskeletal disorders

Hydrotherapy has been studied extensively in chronic pain and rheumatic and musculoskeletal conditions (7).

A systematic review of hydrotherapy for rheumatoid arthritis (RA) suggests positive effects on relieving pain, joint tenderness, and mood symptoms (43). Hydrotherapy as an adjunct to conventional medications in RA patients produced significant changes in oxidative stress biomarkers and activities of antioxidant enzymes suggesting that hydrotherapy can slow disease progression by ameliorating redox status (44).  

In adults with fibromyalgia, pool-based therapy has some additional benefit as compared with either land-based or no physical therapy, with patients undergoing pool-based exercise program having significantly lower pain scores compared to controls (45). Spa therapy and balneotherapy have also been found to improve pain, fatigue, and anxiety, and improve general well-being in fibromyalgia patients (46,47,48,49).

Clinical studies in osteoarthritis (OA) patients demonstrate the benefit of different hydrotherapy treatments: 

• A 2016 Cochrane Review of pool-based therapies for OA, concluded that aquatic exercise may have small, short-term, and clinically relevant effects on patient-reported pain, disability, and quality of life (QoL) in people with knee and hip OA (50). 
• Contrast hydrotherapy has been found to reduce pain and improve QoL in knee osteoarthritis (51) 
• Mineral water baths and hot showers and mineral bath were superior to no treatment for pain, function, stiffness, and quality of life at 3, 6, and 9 months in knee OA patients (52). 
• Hot affusion bath with Epsom salt, three times a week for three weeks significantly reduced pain and stiffness in patients with knee OA, and improved range of motion (53). 
• Several clinical studies have demonstrated the effectiveness of alternating hot and cold compresses with reducing pain and improving function in knee OA patients (54,55).

Immune system support

Although the mechanisms are not entirely understood, both hot and cold hydrotherapy treatments affect innate and adaptive immunity (11,56). Acute cold exposure following pre-heating (18 °C) increased circulation of leucocytes, granulocytes, natural killer cells, and interleukin-6 (IL-6) as mediated by increased noradrenaline (57)

Hot spring (41°C) hydrotherapy significantly increased the total number of leukocytes and lymphocytes in older subjects (>35 years). These increases were related to blood hormonal levels, mainly adrenocortical hormones (58).

Whole-body hyperthermic water bath (immersions) reduced relative total T-lymphocyte counts, increased relative CD8+ lymphocyte and NK cell counts, and activity (59).

In several low-grade inflammation-related pathologies, balneotherapy and mud therapy have anti-inflammatory and chondroprotective effects by reducing serum concentrations of pro-inflammatory cytokines including TNF-α (60,61,62,63), IL-1β (61), and regulatory cytokine IL-6 (64,65), and increased anti-inflammatory growth factor IGF-1 (60,66).

Respiratory disorders

Hydrotherapy can be used to enhance long-term respiratory function by improving vital capacity (VC), thoracic expansion and breathing control (67).

In patients with chronic obstructive pulmonary disease (COPD) the hydrostatic pressure exerted during immersion facilitates expiration and reduces the residual volume, decreasing air trapping (68,69).

Susceptibility to respiratory infections plays a role in exacerbations of COPD. Repeated cold-water stimulations (affusions) reduced the frequency of respiratory infections via immunomodulation relating to Th-1 cells, and improved peak expiratory flow and overall quality of life in COPD patients (70).

Neuroendocrine system support

Various stress factors, including hyperthermia, are known to activate the hypothalamic-pituitary-adrenal (HPA) axis. Hyperthermia-induced activation of the HPA-axis and sympathetic nervous system (SNS) has been reported mostly in healthy subjects undergoing hydrotherapy or sauna baths (71,72) leading to increases in adrenocorticotropic hormone (ACTH) (73), cortisol (73,74), growth hormone (GH) (74,75), prolactin (76,77), β-endorphins (73,77,78), and noradrenaline (NA) (75,76,77,79). 

These neuroendocrine effects are beneficial for inflammatory pain conditions and mood disorders (80,81). In fibromyalgia patients, mud therapy increased levels of ACTH, cortisol and β -endorphin serum levels. The release of these hormones was associated with pain reduction and improved disability, depression, and quality of life (81). Similar effects were observed in OA patients, where an increase in circulating cortisol concentrations was associated with a decrease in the elevated systemic levels of inflammatory cytokines (80).

Cold hydrotherapy is also known to produce similar effects on the HPA axis. Cold stress-induced analgesia is mediated by increased production of opioid peptide beta-endorphin, an endogenous painkiller (82,83).

Mood disorders

Recent studies have demonstrated the psychological effects of hydrotherapy, such as mental relaxation, and improving mental fatigue, quality of life, and depression/stress (84,85,86). Hydrotherapy can exert anxiolytic and antidepressant effects via effects on stress hormones (e.g. cortisol and noradrenaline) (87), β-endorphins and neurotransmitters, including serotonin (88).

Hydrotherapy reduces anxiety symptoms in diagnosed anxiety disorders (89), during labour (90) and in individuals with co-morbidities including chronic myofascial pain syndrome (91); fibromyalgia (92) and chronic heart failure (93).

In an 8-week clinical study involving 237 patients with a generalised anxiety disorder (GAD), balneotherapy significantly improved anxiety scores compared with antidepressant medication (Paroxetine). Remission and sustained response rates were also significantly higher in the balneotherapy group, and improvements in depression scores were also noted (89).

Metabolic conditions

Hydrotherapy may have benefits for improving circulation and insulin resistance in Type 2 diabetes mellitus (TD2M). 

Daily immersion in hot water (37.8°C to 41.0°C) for 3 weeks, as an adjunct to hypoglycaemic medication, was found to improve fasting plasma glucose levels and HbA1c in T2DM patients (94). Improvements in insulin resistance were mediated by increased blood flow to skeletal muscles, where insulin-mediated glucose uptake primarily occurs (94,95).

A single immersion in Dead Sea water produced a significant reduction in blood glucose in T2DM patients, without influencing insulin, cortisol, and c-peptide levels (96).

In type 2 diabetics with mild lower-extremity arterial, 15 weeks of hot spring thermal hydrotherapy combine with acupuncture reduced intermittent claudication symptoms, exerted anti-inflammatory effects, and improved physical function, without significant glycaemic-controlling effects (97).

Daily application of a salt foot bath (40 to 45° for 15 minutes) produced significant reductions in pain scores in patients with painful diabetic peripheral neuropathy (98).