Seawater Pools Versus Freshwater Pools to Treat Inflammatory Skin Diseases and Rheumatic Conditions: A Scoping Review

Seawater is a long-standing remedy against a number of skin or rheumatic conditions since ancient times, now popular in many countries, where spa, thalassotherapy and seawater pools have considerably boomed. Exposure to seawater and sunlight is an essential component of thalassotherapy, defined by any controlled interaction with marine environments and their natural elements, even in the absence of skin applications of algae, sands or muds. Seawater pools therefore offer the opportunity of thalassotherapy to patients unable to go the beach or during the winter months. The evidence from various studies seems to converge on combined exposure to solar radiation and seawater as a more effective approach than irradiation alone or bathing in freshwater followed by irradiation to reduce symptoms of inflammatory skin diseases or rheumatic conditions. An unwanted consequence of chlorine-based treatment of seawater is the formation of DBPs due to reactions of disinfectants with organic matter of anthropogenic origin released by bathers. Whilst chlorination of freshwater predominantly generates chlorinated DBPs, the prevailing DBPs produced by chlorination of seawater pools are brominated DBPs, reportedly more genotoxic. However, despite greater toxicity of brominated DBPs, there is evidence that DBPs concentration in freshwater pools is significantly higher (probably due to the larger number of users) compared to seawater pools. Containing the number of bathers could therefore reduce the risk of exposure to DBPs. The outdoor location of seawater pools can further contribute to reducing the risk of genotoxicity thanks to volatilization, airborne dispersion and photodegradation of some DBPs.