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UV Exposure Beyond Direct Sunlight: What Happens Through Glass and Built Environments
Updated: Aug 3
Ultraviolet exposure is most often discussed in the context of outdoor activity and direct sunlight. This framing, while intuitive, overlooks a substantial proportion of everyday UV exposure that occurs within built environments. Vehicles, offices, and enclosed workspaces do not eliminate ultraviolet radiation. Instead, they alter the spectral composition and pattern of exposure, often shifting it toward longer-duration, lower-intensity UVA.
Understanding this distinction is important when considering cumulative exposure over time, particularly in occupational and daily settings where individuals remain in the same environment for many hours.
UV transmission through glass
Ultraviolet radiation reaching the earth’s surface is composed primarily of UVA and UVB. UVB is strongly associated with erythema and acute sunburn and is largely absorbed by conventional glass. UVA, by contrast, has a longer wavelength, penetrates deeper into the skin, and is transmitted more readily through many glazing materials.
Automotive and architectural glass are typically engineered to reduce UVB transmission for comfort and safety. However, unless specifically treated or laminated for UV control, these materials can allow a meaningful proportion of UVA to pass through. As a result, individuals positioned near windows or inside vehicles may experience sustained UVA exposure without the visual or sensory cues associated with direct sunlight.
Indirect and reflected ultraviolet exposure
In built environments, UV exposure is rarely confined to a single direction or source. Ultraviolet radiation can reflect from surfaces such as asphalt, concrete, water, and metal, contributing to exposure from lateral and oblique angles. This is particularly relevant in environments where individuals are seated or partially shielded from overhead sunlight.
These exposure patterns are subtle and often underestimated. While the intensity at any given moment may be lower than outdoor exposure, the cumulative dose received over extended periods can be significant, especially when exposure occurs daily.
Professions with underestimated cumulative exposure
Certain occupations experience UV exposure profiles that are not traditionally recognised as sun-related. Professional drivers are a clear example. Time spent behind the wheel often involves prolonged exposure through side windows, with consistent exposure of the same skin sites over many hours.
Similar exposure patterns can occur in other roles, including operators of enclosed machinery, personnel working in site offices with extensive glazing, and workers who alternate between indoor and outdoor environments throughout the day. In these contexts, UV exposure is characterised less by intensity and more by duration, repetition, and asymmetry.
Implications for protection strategies
Most public guidance on sun protection is oriented toward short periods of high-intensity exposure. Long-duration exposure dominated by UVA presents a different set of considerations. Protection strategies in these settings must provide broad-spectrum coverage and maintain effectiveness over time, even when reapplication is infrequent or impractical.
This has direct relevance to the selection of UV filters, particularly in occupational or daily-use products intended for prolonged wear.
Technical summary
Quantitative evidence supports the role of vehicle glass in altering ultraviolet exposure, particularly with respect to UVA transmission. A 2025 study by AlQahtani et al., published in Frontiers in Public Health, measured UV irradiance inside and outside 20 vehicles using a calibrated data-logging radiometer, comparing transmission through front windshields and side windows.
The study found that windshields reduced UV levels substantially, with average irradiance behind the windshield measuring around 8% of the level recorded outside the vehicle, roughly 92% attenuation. Side windows offered meaningfully less protection, with average irradiance inside measuring around 21% of the outside level, more than double the exposure allowed through the windshield. This is consistent with side windows typically using tempered glass, which lacks the UV-blocking interlayer found in laminated windshield glass (AlQahtani et al., 2025).
These findings show that while vehicle windshields substantially reduce UV exposure, side windows provide meaningfully less protection, a relevant consideration for occupations involving extended time in vehicles, such as professional driving.
Mineral UV filters in long-duration exposure scenarios
Exposure scenarios dominated by UVA place emphasis on photostability and persistence at the skin surface. Non-nano zinc oxide powder is a mineral UV filter that reflects and scatters both UVA and UVB rather than relying on photochemical absorption. This physical mode of action contributes to its stability under prolonged exposure, an advantage in settings where reapplication is infrequent or impractical.
For situations involving extended time in vehicles or near glazing, mineral filters such as non-nano zinc oxide are often well suited due to their broad-spectrum coverage and consistent performance. Advance ZincTek manufactures non-nano zinc oxide for sunscreen and skincare formulations intended to align with these exposure patterns, supporting protection in built environments where UVA dominates cumulative exposure.
Learn more about Australian-manufactured non-nano zinc oxide and how Advance ZincTek supports sun protection across everyday and high-UV environments.
References
AlQahtani, N. J., AlEssa, G. N., AlDushaishi, H. F., Bukair, A. N., & Ali, S. M. (2025). Assessment of ultraviolet and infrared radiation transmission through automobile windshields and side windows. Frontiers in Public Health, 12, 1497357. https://doi.org/10.3389/fpubh.2024.1497357
Diffey, B. L. (2002). Sources and measurement of ultraviolet radiation. Methods, 28(1), 4–13. https://doi.org/10.1016/S1046-2023(02)00204-9
Gasparro, F. P., Mitchnick, M., & Nash, J. F. (1998). A review of sunscreen safety and efficacy. Photochemistry and Photobiology, 68(3), 243–256. https://doi.org/10.1111/j.1751-1097.1998.tb02487.x
