Rash guard vs swim shirt

A rash guard is cut close to the body so it does not drag in water — it was designed for surfers, to prevent board rash. A swim shirt is a looser version of the same idea, more comfortable on land and cooler in still air. Both can be UPF 50+, and the UPF rating matters far more than which word is on the label. Buy a rash guard if you will be swimming or surfing, a swim shirt if you will mostly be on the sand.

Where the names come from

A rash guard was originally exactly what it sounds like: a shirt worn under or instead of a wetsuit to stop a surfboard rubbing the chest and stomach raw. Sun protection was a side effect that became the main selling point. The close fit is a surfing requirement, not a style choice.

A swim shirt is the same fabric idea in an ordinary shirt cut, sold to people who want sun cover at a pool or on a beach rather than performance in surf. Retailers use the two terms interchangeably, which is why the distinction is worth knowing before you order online.

Which to buy

Buy a rash guard if

• You will be swimming, surfing, bodyboarding or snorkeling, where drag is a real problem.
• It is for a child who will be in and out of water all day — a loose shirt fills with water and pulls.
• You want something that stays put rather than riding up and exposing the lower back.

Buy a swim shirt if

• You will mostly be on the sand or by the pool rather than in the water.
• You want something cooler in still air — looser fabric moves more air.
• You will wear it over swimwear as a cover-up and want it to look like a normal shirt.
• The close fit of a rash guard is uncomfortable, which for many people it simply is.

What matters more than either

The UPF rating. A close-fitting rash guard in a thin, unrated fabric protects less than a loose swim shirt rated UPF 50+. Look for a stated rating, and ideally the words rated wet or dry — purpose-built UPF synthetics hold their rating when wet, and ordinary cotton loses a large share of its already-low protection. Does UPF clothing work wet.

After that: sleeve length, because short sleeves leave the forearms — a high-exposure area — uncovered; and whether there is a hood, which covers the back of the neck.

Fit, for both

Close-fitting, not tight. Stretching a fabric opens the gaps between fibers and lets more UV through, so a rash guard straining across the chest protects less than one that fits properly. The test: a flat hand should slide between the fabric and the chest, and the hem should stay put when both arms go up. Rash guard fit guide.

For loose swim shirts the opposite risk applies — too loose and it rides up in water or flaps enough to expose skin repeatedly.

Care, which is the same for both

• Rinse in fresh water after salt or chlorine, every time.
• Wash cool and line dry. Hot tumble drying degrades elastane faster than anything else you will do to it.
• Skip fabric softener, which coats fibers and reduces the fabric's ability to move moisture.
• Replace when it goes thin or slack. Fabric-based UPF does not wash out, but a worn-out garment has lost protection regardless.