The short answer to whether you can get sunburnt through glass is both yes and no, depending on the type of skin damage. True sunburn, the immediate, painful reddening of the skin, is largely prevented by standard window glass. However, the radiation responsible for long-term skin aging and increased cancer risk can still pass through the glass barrier with relative ease. This interaction is determined by the distinct properties of the two primary types of ultraviolet (UV) light that reach the Earth’s surface.
Understanding the Two Types of Ultraviolet Light
The sun produces ultraviolet radiation, invisible energy categorized by wavelength. The two main types relevant to skin health are Ultraviolet B (UVB) and Ultraviolet A (UVA) light. UVB rays are shorter in wavelength and primarily affect the outer skin layers (epidermis). This higher-energy radiation is the main cause of painful sunburn and plays a significant role in most skin cancers.
UVA rays possess a longer wavelength, allowing them to penetrate much deeper into the skin, reaching the dermis layer. UVA is the primary contributor to premature aging, causing wrinkles, sun spots, and the breakdown of collagen. While UVB intensity fluctuates throughout the day, UVA rays are more constant throughout daylight hours and make up about 95% of the UV radiation that reaches the Earth’s surface. Both types of UV light cause harm by damaging the DNA in skin cells.
The Barrier Effect of Standard Glass
Standard window glass, such as the soda-lime-silica glass used in homes and offices, is an effective yet incomplete UV filter. This glass naturally absorbs or reflects almost all shorter-wavelength UVB rays. Studies show that clear glass can block between 90% and 99% of UVB radiation, which is why sitting by a window rarely results in a noticeable sunburn.
This high level of UVB filtration means the radiation responsible for immediate skin reddening is mostly stopped at the glass pane. However, the longer wavelength of UVA light allows it to bypass this barrier with ease. A significant portion of UVA radiation, often ranging from 50% to 75%, transmits through clear glass and reaches the skin indoors.
The differential blocking capability is the reason for the nuanced answer to the question of sun exposure through glass. The glass effectively prevents the sunburn caused by UVB, but it provides limited defense against the deep-penetrating, aging effects of UVA. This continuous, low-level exposure poses a chronic risk to skin health for those spending long periods near untreated windows. Specialized glass, such as laminated glass or glass with UV-blocking films, offers a much higher level of protection against both UVA and UVB rays.
Cumulative Exposure in Everyday Settings
The partial protection offered by standard glass translates into a risk of chronic, cumulative UVA exposure in many everyday environments. A common scenario is prolonged time spent driving, where one side of the body is often exposed to unfiltered sunlight for years. The side windows of many cars are made of tempered glass, which provides minimal protection against UVA. This often leads to visible signs of asymmetric aging, such as deeper wrinkles and sun spots, on the driver’s side arm and face.
The front windshield of most modern vehicles is typically made with laminated glass, which includes a plastic interlayer that blocks nearly 100% of both UVA and UVB rays. However, this advanced protection is often not extended to the side and rear windows, leaving occupants exposed to UVA. Similarly, sitting near a sunny window for hours while working from home or in an office exposes the skin to a low but constant dose of UVA radiation.
To mitigate this chronic exposure, several practical steps can be taken to reduce the risk of long-term damage:
- Applying a broad-spectrum sunscreen, which protects against both UVA and UVB, is recommended even when remaining indoors near windows.
- Installing UV-blocking window films on existing glass can be a cost-effective solution, as these films are designed to block up to 99.9% of UV radiation.
- Opting for specialized glass, such as laminated or low-emissivity (Low-E) coated windows, when replacing glass can significantly reduce the amount of harmful UVA transmission.