A tan is the skin’s biological defense mechanism, where skin cells produce the pigment melanin in response to damage caused by ultraviolet (UV) radiation. This natural darkening signals exposure to the sun’s harmful rays. The common idea that water provides complete shelter from this process is incorrect. The short answer is definitively yes, you can get a tan in water, and the aquatic environment introduces unique factors that can intensify the sun’s effect. Understanding the physics of light and the body’s sensory response is important for safe time spent near or in the water.
How UV Light Penetrates Water
UV radiation (UVA and UVB rays) is not entirely blocked by water. Both types transmit through the water column, allowing exposure to continue even when the body is submerged. The amount of UV that reaches the skin depends heavily on the water’s clarity and depth. In clear ocean water, measurable UVB can be detected up to 16 meters deep, and UVA penetrates even further. While murky water absorbs UV light more quickly, the UV threat remains present in typical swimming pools or clear seas.
The Intensifying Effect of Surface Reflection
The water’s surface does more than simply allow UV light to pass through; it also acts as a reflective surface, significantly increasing the overall radiation dose. Solar radiation strikes the water from above, but a portion is scattered and reflected back upwards toward the skin. This effect makes being near water more dangerous than being on dry land, as the skin is bombarded with UV rays from two directions. While still water reflects approximately 10% of UV radiation, sea foam can reflect up to 25%. When floating or swimming, the exposed body parts receive full overhead sun exposure plus this reflected radiation, which is particularly intense on the face, neck, and shoulders.
Why Water Masks Sunburn
A major reason people experience severe sunburn after spending time in the water is the masking effect of the liquid medium. Sunburn is an inflammatory reaction to UV damage, typically signaled by heat and tenderness. The constant cooling effect of the water prevents the skin’s temperature sensors from registering this heat and the early signs of burning. This lack of a sensory warning allows for extended exposure times, resulting in a burn that only becomes noticeable hours later after the person has dried off. To counter this delayed warning system, applying a broad-spectrum, water-resistant sunscreen with a high Sun Protection Factor (SPF) is necessary, with reapplication every 40 to 80 minutes depending on the product’s resistance rating.