Tanning is the skin’s reaction to exposure to ultraviolet (UV) radiation. This biological process is triggered by UVA and UVB rays, and water does not stop these rays from reaching the skin. The idea that being submerged in a pool provides complete protection from the sun’s rays is a common and dangerous misconception.
UV Radiation’s Journey Through Pool Water
Ultraviolet light, which includes the skin-damaging UVA and UVB wavelengths, does not simply stop at the water’s surface. A significant portion of this radiation is transmitted through the water column. Clear pool water, which is low in dissolved organic matter and other light-blocking particles, is a poor filter for UV energy.
The longer wavelength UVA rays penetrate water more effectively than the shorter UVB rays, reaching deeper into the skin layers. Studies indicate that even at a depth of half a meter (about 1.6 feet) in clear water, the UV intensity can remain at approximately 40% of the surface level. At three feet below the surface, the water only blocks about 20% of the incoming UV rays, meaning skin is still exposed to a substantial dose of radiation even when fully submerged.
The degree of UV transmission depends on the water’s clarity, but in a typical, well-maintained pool, the protection offered by depth is minimal. Relying on the water itself to shield the skin is not an effective sun safety strategy.
The Increased Risk From Surface Reflection
Being in or near a pool introduces a unique amplification of UV exposure through reflection. Water acts as a reflective surface, bouncing a portion of the incoming UV light off the surface and the pool bottom toward the swimmer. While water typically reflects 5% to 10% of UV, this reflection hits the skin from multiple angles simultaneously.
This multi-directional exposure means that areas of the body usually shadowed from direct overhead sun, such as the underside of the chin or arms, are now receiving UV radiation. Wet skin itself can also increase a person’s susceptibility to sun damage. When skin is wet, it may be more prone to UV penetration. The constant cycle of getting in and out of the water, combined with towel drying, can quickly degrade or rub off applied sunscreen.
Practical Sun Safety for Swimmers
Swimmers should use a broad-spectrum, water-resistant sunscreen with a Sun Protection Factor (SPF) of at least 30. A sufficient amount, generally about one ounce for an adult’s full body, should be applied approximately 15 minutes before entering the water to allow it to bind to the skin.
Due to the effects of water and friction, sunscreen reapplication must be more frequent than on dry land. Even “water-resistant” formulas only maintain their stated SPF for 40 or 80 minutes while swimming, requiring reapplication immediately after that time, or at least every two hours. Wearing protective clothing, such as rash guards with a high Ultraviolet Protection Factor (UPF), provides a reliable physical barrier against both direct and reflected rays.
Seeking shade is a simple preventative measure, especially during the peak UV hours between 10 a.m. and 4 p.m. Taking breaks from the water and resting under an umbrella or canopy can significantly reduce the cumulative UV exposure over a day of swimming.