When people ask if water “attracts” the sun, they are trying to understand why they get sunburned easily while swimming or boating. The sun’s energy, which includes visible light and invisible ultraviolet (UV) radiation, is not magnetically drawn to water. Instead, the interaction is governed by physics: how light is transmitted, absorbed, and reflected by the water medium. This process ultimately intensifies our exposure to UV rays, which are the primary cause of sunburn and skin damage.
The Physics of Light and Water
Water acts as a medium that alters the light’s path and intensity. When solar radiation strikes the surface, it undergoes three primary processes: transmission, absorption, and reflection. Transmission is when light passes through the water, while absorption converts light energy into heat. Visible light transmits well through clear water, especially blue and green wavelengths, which is why oceans appear blue.
The absorption rate is not uniform across the electromagnetic spectrum; water strongly absorbs infrared and some UV wavelengths. This selective absorption means different colors of light penetrate to different depths. For instance, longer red wavelengths are absorbed almost immediately. The third process, reflection, causes the dazzling glare on the water and increases sun exposure.
Understanding UV Penetration
Ultraviolet radiation (UV), the invisible part of sunlight responsible for sun damage, is divided into UVA and UVB rays, and both can travel surprisingly far below the surface. Water is an effective filter of the shorter UVB wavelengths, but a significant portion still penetrates. Studies indicate that up to 50% of the surface UVB can be present one meter below the water’s surface, particularly in clear water.
The longer-wave UVA rays penetrate much deeper into the water column. As much as 80% of UVA radiation can reach one meter below the surface, meaning submerged skin is vulnerable to damage. The total depth of UV penetration is heavily influenced by factors like water clarity, dissolved organic matter, and turbidity. UV penetrates deeper in the clear, open ocean than in murky coastal waters. For example, in highly transparent ocean areas, the depth where only 10% of surface UVB remains can be up to 16 meters, while for UVA, it can reach 46 meters.
The Role of Surface Reflection
The most significant factor amplifying sun exposure near water is the reflective property of the water’s surface. The smooth surface acts like a mirror, bouncing UV radiation upwards and increasing the total radiation hitting the skin. This reflection occurs in addition to the direct UV rays from the sun overhead, effectively creating a double dose of exposure. The water surface reflects between 5% and 10% of incident UV rays, directing them toward areas like the chin, neck, and face that are typically less exposed.
When the sun is overhead, reflection is most intense, and the combination of direct and reflected light significantly raises the overall UV index. This amplified exposure causes people to get sunburned faster when swimming, even if partially submerged. The reflective effect is enhanced near other bright surfaces, such as light-colored sand, which can reflect up to 15% of UV rays. This means exposure occurs even when standing under a beach umbrella.
Water’s Effect on Body Temperature and Sensation
The physical cooling sensation of water causes people to overlook sun safety, as it suppresses the body’s natural warning signs. When skin is exposed to the sun’s heat, nerve endings signal the need to seek shade. Immersion in cool water constantly cools the skin’s surface, masking this thermal warning sign.
The lack of heat sensation tricks the individual into feeling comfortable and safe, leading to longer sun exposure times. People often do not realize they are burning until they are out of the water and the skin begins to feel hot and painful. This delayed awareness of sun damage is a major contributor to severe sunburns experienced during water activities. The cooling effect prevents the immediate feedback loop between sun exposure and heat, making it easier to accumulate significant UV damage.