Ultraviolet (UV) radiation from the sun causes sunburn, a form of skin damage resulting from overexposure. Many people who spend time in or near water report getting burned much faster than on dry land. This raises the question of whether water accelerates the biological process of sunburn, or if other factors are involved. The aquatic environment creates conditions that significantly amplify the total UV dose the skin receives.
Why People Feel They Burn Faster
The sensation of a rapid sunburn near water is primarily due to a deceptive cooling effect that masks the immediate signs of heat. When swimming or sitting near the water, evaporation and direct contact with the cooler liquid draw heat away from the skin. This cooling prevents the body from providing the typical sensory feedback that warns a person they are overheating from sun exposure.
Because the skin is not registering the usual heat, people tend to remain exposed for significantly longer periods. This extended, unnoticed exposure time is the major reason for the severe burns often experienced after a day on the water. The cooling sensation provides a false sense of security, leading to a much higher cumulative dose of UV radiation.
The Physics of Water and UV Exposure
The physical interaction between water and sunlight increases the overall UV dose reaching the skin. Water acts as a reflective surface, enhancing exposure through the albedo effect. While water has a relatively low reflection rate, a calm surface can bounce up to 10% of the incident UV rays back onto the skin. This reflection acts as a secondary source of radiation, providing a double dose of UV light to exposed areas.
The skin remains vulnerable to UV damage even when submerged beneath the surface. Water does not block UV radiation as effectively as shade or solid materials. In clear water, UV-A and UV-B rays can penetrate to significant depths. UV-B remains detectable at depths of 10 meters (about 30 feet) or more in the clearest ocean conditions. The clarity of the water, determined by elements like dissolved organic matter and turbidity, dictates the exact depth of penetration, meaning remaining just below the surface provides only partial protection.
Protecting Skin During Water Activities
Protection during water activities must account for both the increased physical exposure and the deceptive cooling sensation. Sunscreen remains an important defense, but application must be managed carefully since water washes the product away. When choosing sunscreen for swimming, look for formulas specifically labeled as “water-resistant.” This indicates they maintain their Sun Protection Factor (SPF) for either 40 or 80 minutes while immersed, based on regulatory testing.
Reapplication is necessary immediately after swimming, sweating, or using a towel. It should not be delayed until the 40 or 80-minute window is complete. Even durable formulas should be reapplied at least every two hours to maintain consistent protection.
Physical barriers provide the most reliable defense against the amplified UV environment. Seeking shade, especially during the peak sun hours between 10 a.m. and 4 p.m., is recommended.
Wearing physical coverings such as wide-brimmed hats and rash guards with a high Ultraviolet Protection Factor (UPF) rating offers continuous protection that cannot be washed or sweated away. Actively taking breaks from the sun and moving out of the water to cool down helps the body register its thermal state. Counteracting the cooling effect helps prevent the prolonged, unnoticed exposure that leads to severe sunburn.