A rash guard, also known as rash vest or rashie, is a type of water wear, an athletic shirt

Shirt

A shirt is a cloth garment for the upper body. Originally an undergarment worn exclusively by men, it has become, in American English, a catch-all term for almost any garment other than outerwear such as sweaters, coats, jackets, or undergarments such as bras, vests or base layers...

 made of spandex

Spandex

Spandex or elastane is a synthetic fibre known for its exceptional elasticity. It is strong, but less durable than natural Latex, its major non-synthetic competitor. It is a polyurethane-polyurea copolymer that was co-invented in 1959 by chemists C. L. Sandquist and Joseph Shivers at DuPont's...

 and nylon

Nylon

Nylon is a generic designation for a family of synthetic polymers known generically as polyamides, first produced on February 28, 1935, by Wallace Carothers at DuPont's research facility at the DuPont Experimental Station...

 or polyester

Polyester

Polyester is a category of polymers which contain the ester functional group in their main chain. Although there are many polyesters, the term "polyester" as a specific material most commonly refers to polyethylene terephthalate...

. The name rash guard reflects the fact that the shirt protects the wearer against rashes caused by abrasion. These shirts can be worn by themselves, or under a wetsuit

Wetsuit

A wetsuit is a garment, usually made of foamed neoprene, which is worn by surfers, divers, windsurfers, canoeists, and others engaged in water sports, providing thermal insulation, abrasion resistance and buoyancy. The insulation properties depend on bubbles of gas enclosed within the material,...

. A rash guard by itself is used for light coverage in warm to extreme summer temperatures for several watersports including surfing

Surfing

Surfing' is a surface water sport in which the surfer rides a surfboard on the crest and face of a wave which is carrying the surfer towards the shore...

, scuba diving

Scuba diving

Scuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater....

, snorkelling, freediving, wakeboarding

Wakeboarding

Wakeboarding is a surface water sport which involves riding a wakeboard over the surface of a body of water. It was developed from a combination of water skiing, snow boarding and surfing techniques....

, body surfing, body boarding, windsurfing

Windsurfing

Windsurfing or sailboarding is a surface water sport that combines elements of surfing and sailing. It consists of a board usually two to four metres long, powered by the orthogonal effect of the wind on a sail. The rig is connected to the board by a free-rotating universal joint and comprises a...

, kitesurfing

Kitesurfing

Kitesurfing or Kiteboarding is an adventure surface water sport that has been described as combining wakeboarding, windsurfing, surfing, paragliding, and gymnastics into one extreme sport. Kitesurfing harnesses the power of the wind to propel a rider across the water on a small surfboard or a...

, kayaking

Kayaking

Kayaking is the use of a kayak for moving across water. Kayaking and canoeing are also known as paddling. Kayaking is distinguished from canoeing by the sitting position of the paddler and the number of blades on the paddle...

, or simply for stand up paddle surfing

Stand up paddle surfing

Stand up paddle surfing , or in the Hawaiian language Hoe he'e nalu, is an emerging global sport with a Hawaiian heritage. The sport is an ancient form of surfing, and reemerged as a way for surfing instructors to manage their large groups of students, as standing on the board gave them a higher...

 or swimming. There are also lower body rash guards, which are similar to compression shorts

Compression shorts

Compression shorts are undergarments usually worn by athletes. They are form-fitting garments and when worn cover the athlete's waist to mid or lower thigh. These garments are often made from a spandex-type material, similar to cycling shorts....

 to be worn under the surfers' boardshorts, but more specialized for surfers. The most specialized version is called the Elephant Surf Trunks, while some companies make less specialized versions.

Rash guards are most often worn in surfing when the weather is too warm for a wetsuit

Wetsuit

A wetsuit is a garment, usually made of foamed neoprene, which is worn by surfers, divers, windsurfers, canoeists, and others engaged in water sports, providing thermal insulation, abrasion resistance and buoyancy. The insulation properties depend on bubbles of gas enclosed within the material,...

, and to prevent wax-based chafing from sliding on and off of the surf board, on either the torso, or the legs. A surfboard's wax holds sand from the beach that could rub against a surfer's torso while paddling out to the break, or legs while sitting atop one's board. Rash guards also offer some protection from the sun (measured by its Ultraviolet Protection Factor) and slight protection against jelly fish stings and are sometimes worn under wetsuits to prevent chafing

Chafing

Chafing when used as a nautical term describes the process of wear on a line or sail caused by constant rubbing against a hard, usually metallic, surface. Various methods are used to prevent chafing. Chafing of lines that rest on a choke on a boat can be prevented by putting a protecting material...

. A rash guard helps to prevent irritation caused by rapid impact with surface water and waves as well.

Rash guards are thought to have originated in Australia

Australia

Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

, where they are commonly referred to as "rashies" or "rashys." Variations of the rash guard have made their way into many other sports including baseball

Baseball

Baseball is a bat-and-ball sport played between two teams of nine players each. The aim is to score runs by hitting a thrown ball with a bat and touching a series of four bases arranged at the corners of a ninety-foot diamond...

, American football

American football

American football is a sport played between two teams of eleven with the objective of scoring points by advancing the ball into the opposing team's end zone. Known in the United States simply as football, it may also be referred to informally as gridiron football. The ball can be advanced by...

, water polo

Water polo

Water polo is a team water sport. The playing team consists of six field players and one goalkeeper. The winner of the game is the team that scores more goals. Game play involves swimming, treading water , players passing the ball while being defended by opponents, and scoring by throwing into a...

, Brazilian Jiu Jitsu, and Mixed Martial Arts

Mixed martial arts

Mixed Martial Arts is a full contact combat sport that allows the use of both striking and grappling techniques, both standing and on the ground, including boxing, wrestling, Brazilian jiu-jitsu, muay Thai, kickboxing, karate, judo and other styles. The roots of modern mixed martial arts can be...

.

Other important components of a rash guard include flatlock stitching, and six panel construction. Flatlock stitching creates a seam where the seam allowances lies flat to the garment instead of hanging loose from it. It is made by adjusting the overlock or the thread overedge stitch. Flatlock stitching increases the strength of the garment for intense exercise or recreational activities. Six panel construction versus the conventional 4 panel tee shirt construction enables the user increased mobility wet or dry.

The combination of products used to construct a rash guard differ slightly depending on the designer. The use of nylon and spandex create a garment that is lightweight, quick drying, flexible, durable, naturally antibacterial and water wicking.

Swim shirts

Swim shirts are relatively new to the consumer market, but are growing in popularity. They are generally more loose fitting and casually worn. Their primary purpose is to offer an alternative to sunscreen to protect the wearer's skin from the sun's UV radiation and possible skin cancer

Skin cancer

Skin neoplasms are skin growths with differing causes and varying degrees of malignancy. The three most common malignant skin cancers are basal cell cancer, squamous cell cancer, and melanoma, each of which is named after the type of skin cell from which it arises...

. Many swim shirts carry a UPF

UPF

UPF may refer to:*Universitat Pompeu Fabra, a university in Spain*Université de la Polynésie Française, a university in Tahiti*United People's Front of Nepal, a political organization...

 rating of 50+, which blocks out over 98% of the sun’s harmful rays. Many people find that sunscreen isn’t always enough because it is often not used properly and some have skin allergies or sensitivities to chemicals that sunscreens may contain.
Swim shirts may also be used by overweight people, to cover up the belly area and other parts of the body, that may embarrass the person.
Even though the name generally applies to water sports, people use swim shirts for an array of activities: swimming, boating

Boating

Boating is the leisurely activity of travelling by boat, or the recreational use of a boat whether powerboats, sailboats, or man-powered vessels , focused on the travel itself, as well as sports activities, such as fishing or water skiing...

, golfing, tennis

Tennis

Tennis is a sport usually played between two players or between two teams of two players each . Each player uses a racket that is strung to strike a hollow rubber ball covered with felt over a net into the opponent's court. Tennis is an Olympic sport and is played at all levels of society at all...

, gardening

Gardening

Gardening is the practice of growing and cultivating plants. Ornamental plants are normally grown for their flowers, foliage, or overall appearance; useful plants are grown for consumption , for their dyes, or for medicinal or cosmetic use...

, playing in the sprinklers, water parks, beach trips, pool play, rivers and lakes, water skiing

Water skiing

thumb|right|A slalom skier making a turn on a slalom waterski.Waterskiing is a sport where an individual is pulled behind a boat or a cable ski installation on a body of water, skimming the surface.-History:...

, surfing, snow skiing, sledding

Sledding

Sledding , sledging , sleding or tobogganing is a common activity in wintry areas, similar to sliding, but in a prone or seated position requiring a device or vehicle generically known in the US as a sled or in other countries as a sledge or toboggan...

, skimboarding, and even in martial arts (to protect from practitioners rashes caused by the keikogi

Keikogi

or dōgi is a uniform for training, used in martial arts derived from Japan, or budō. . The prototype for the modern keikogi emerged in the late 19th century. The keikogi was developed by judo founder Kano Jigoro...

).