Sea bathing is swimming in the sea or in sea water and a sea bath is a protective enclosure for sea bathing. Unlike bathing in a swimming pool, which is generally done for pleasure or exercise purposes, sea bathing was once thought to have curative or therapeutic value. It arose from the medieval practice of visiting spas for the beneficial effects of the waters. The practice of sea bathing dates back to the 17th century but became popular in the late 18th century. The development of the first swimsuits dates from the period as does the development of the bathing machine.

The practice of sea-bathing developed starting in the mid-1800s into the modern cultural phenomenon of beachgoing. In the 19th century, the introduction of railways led to the further development of seaside resorts and bathing boxes. The death of large numbers of people while swimming in the open sea led to the introduction of surf lifesaving in Australia and lifeguards throughout the world in the early 20th century. With the extension of scheduled air transport since the latter half of the 20th century, the development of seaside resort areas such as Ibiza in Spain, the Queensland Gold Coast in Australia and the Miami metropolitan area in the U.S. attracted millions of visitors annually.

The growth in popularity of sea bathing developed from the perceived health benefits of mineral springs, such as those at Spa in Belgium, Bath in England and Aachen in Germany. Sea water was similarly believed to have medicinal benefits. The medicinal benefits of the sun were also being recognised.

In 1753, Dr. Richard Russell published The Use of Sea Water which recommended the use of sea water for healing various diseases, and William Buchan wrote his 1769 book Domestic Medicine advocating the practice. Sea bathing and sea water were advocated with winter considered to be the best time to follow the practice. Buchan's book was published until 1846 and was translated into many languages.

Marine hospitals opened in parts of France and England. The first French marine hospital, Petit Berck, opened in 1861.

There has been a tremendous growth in sea bathing, especially in the 20th century. However, the trend was slightly reversed after melanoma was linked with excessive exposure to the sun.^{[citation needed]}

Though no longer widely considered to actually cure disease, shades of the supposed curative properties of sea water can still be noted with the trend of bath products containing Dead Sea salt, which is claimed to provide some relief from certain skin diseases.

With Buchan's recommendations, people suddenly flocked to the coasts, especially to Great Britain and France. The public and authorities were concerned with the morality of general sea bathing. Scarborough was the first resort to introduce bathing machines, with a John Setterington engraving showing machines in 1735. They were soon adopted in most of the aspiring English seaside resorts. Women would wear "bathing gowns" in the water while the men would wear long swimsuits. Some resorts such as Margate had modesty hoods or tilts which were canvas awnings attached to bathing machines. These could be let down to allow a woman to enter and leave the water in privacy. If desired, the woman could also be dipped in privacy under the shelter of the hood.