The answer is yes, you can absolutely get a suntan in the shade, and you can also get a sunburn. Tanning is the body’s defensive response to damage from invisible ultraviolet (UV) radiation, which is present even when direct sunlight is blocked. The goal of sitting in the shade is to reduce the intensity of this radiation, but it does not eliminate exposure entirely. Understanding that UV rays can reach you indirectly is the first step toward effective sun protection.
How Ultraviolet Radiation Causes Tanning
Tanning is a biological process where skin cells, specifically melanocytes, produce a brown pigment called melanin. This melanin acts as a natural, albeit limited, sunblock by absorbing UV radiation and dissipating the energy as heat. Melanin protects the underlying cellular DNA from damage. The darkening of the skin is a visible sign of this protective mechanism being activated.
Ultraviolet radiation is categorized into different wavelengths, with two primary types affecting the skin: UVA and UVB. UVA rays penetrate deep into the dermis layer, primarily causing long-term aging and contributing to the oxidation of existing melanin, which results in the immediate, short-lived tan. UVB rays are shorter and affect the epidermis, or outer layer, and are the main cause of sunburn and the delayed, more lasting melanin synthesis response.
The body’s production of new melanin begins roughly 24 to 48 hours after UV exposure and continues for several weeks, creating the deeper, more sustained tan. While UVB is the primary driver for this new melanin production, UVA rays also play a role in promoting the distribution of the pigment.
The Physics of Shade: Scattering and Reflection
Shade effectively blocks the direct UV rays traveling in a straight line from the sun to your skin, but this direct light is only one component of total UV exposure. The main reason you can still tan in the shade is due to two physical phenomena: atmospheric scattering and surface reflection. A significant amount of UV light is scattered by molecules and aerosols in the atmosphere, making the entire sky a source of radiation.
This scattered UV light, often called “skylight,” is diffuse and can reach you from every direction, bypassing the overhead shade structure. Even with a dense umbrella, you are still exposed to this ambient UV light from the open sky around you. The amount of scattering is greater for shorter wavelengths, meaning the more damaging UVB rays are scattered more efficiently than UVA.
Reflection is the second major source of UV exposure in the shade, where UV light bounces off nearby surfaces onto your skin. Shade structures do nothing to stop rays that have already hit the ground or a wall. Surfaces like sand, water, and snow act like mirrors, redirecting the UV radiation into the shaded area.
Environmental Factors Affecting Shade Exposure
The surrounding environment greatly influences the intensity of reflected UV light reaching a person in the shade. Highly reflective surfaces drastically increase total UV exposure. Fresh snow is the most reflective natural surface, bouncing back up to 80% of UV radiation, making sun protection necessary even in the shade during winter activities.
Water reflects a substantial amount of UV light, ranging from 5% to 10% when the sun is high, and increasing up to 30% at oblique angles. Dry sand reflects around 17% of UV rays. Concrete and light-colored paint on buildings also serve as significant reflectors, increasing the ambient radiation load under an awning or umbrella.
The time of day also affects shade exposure because the sun’s intensity peaks between 10 a.m. and 4 p.m. During these hours, the scattered and reflected UV is at its strongest, meaning a person in the shade is still receiving a higher dose of radiation. Not all shade is equal; a thin umbrella provides less protection than deep shade created by a solid building or a dense canopy.
Strategies for Protection When Out of Direct Sun
Protection is necessary even when seeking shelter from direct sunlight to mitigate the risk from scattered and reflected UV. The following strategies help minimize exposure:
- Apply broad-spectrum sunscreen with an SPF of at least 30 to all exposed skin. Broad-spectrum protection filters both UVA and UVB rays.
- Reapply sunscreen generously every two hours, or immediately after swimming or heavy sweating, as effectiveness is diminished by water and friction.
- Wear protective clothing, especially when near highly reflective surfaces like water or sand. Look for clothes with an Ultraviolet Protection Factor (UPF) rating.
- Use hats with a wide brim (three inches or more) to shield the face, ears, and neck from overhead and ambient light.
- Wear wrap-around sunglasses that block 99% to 100% of both UVA and UVB rays to protect the eyes and surrounding skin.
- Choose “deep shade,” such as a fully enclosed area or a dense cluster of trees, to further minimize exposure by blocking surrounding skylight.