Although the mechanisms by which spa therapies alleviate certain diseases are still being deciphered, most scientists agree that they probably have chemical, thermal, mechanical and immunological components. Let's look at each in more detail.
Chemical effects. The chemical composition of water used in balneotherapy varies greatly, depending on the source. Sulfur, present in "sulfur waters" as a free or combined ion, is one of the most common chemicals in mineral spa waters. It is known to promote keratolysis, the loosening and shedding of the outer layer of the skin, which can be effective in treating certain skin conditions, such as acne. It also possesses antibacterial and antifungal properties, believed to be the result of sulfur interacting with reactive oxygen molecules in the epidermis to produce an acidic environment that prevents microbe growth.
Other minerals act differently. Magnesium, for example, inhibits the synthesis of polyamines, essential molecules in eukaryotic cells. Polyamines are thought to play a role in the development of psoriasis. When patients with psoriasis soak in water with high magnesium concentrations, they often see an improvement in their conditions.
Thermal effects. Hot water has several beneficial effects. Heat increases the concentration of beta-endorphin, a natural painkiller. In addition to its analgesic effects, beta-endorphin boosts the immune system, slows the growth of cancer cells and increases relaxation.
Heat also prevents inflammation, probably by increasing the secretion of cortisol and catecholamines, two hormones produced by the adrenal glands. For this reason, doctors often prescribe hot-water baths to treat inflammatory conditions, such as arthritis or dermatitis, as well as certain autoimmune diseases.
Mechanical effects. An immersed body experiences a force applied by the water on all sides. This force is known as hydrostatic pressure and can have many benefits. In the lower legs and feet, which are deeper and feel a greater force, it reduces swelling, decreases blood pooling and helps to return venous blood to the heart. Hydrostatic pressure may also contribute to lower working heart rates while in the water.
Buoyancy, the upward vertical force of water on a submerged body, is another important mechanical effect. Buoyancy counteracts the effects of gravity and reduces compression of the joints. Many people who can't exercise on land bearing their full weight can exercise vigorously and comfortably in water.
Immunological effects. Some research suggests that trace elements present in mineral water are absorbed through the skin and affect the immune system. Sulfur water is believed to inhibit proliferation of certain lymphocytes and their ability to produce and release cytokines. Cytokines are proteins that help regulate the immune response. For example, patients with rheumatoid arthritis produce an excess of interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha), two important cytokines. By inhibiting IL-1 and TNF-alpha, sulfur water may relieve symptoms of arthritis and other inflammatory diseases.