UV Exposure Beyond Direct Sunlight: What Happens Through Glass and Built Environments

Geoff Acton
20 hours ago
4 min read

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.

non nano zinc oxide — Image Sourced: https://irishskin.ie/2025/05/20/surprising-things-solar-uv-can-pass-through/

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 2024 observational study by Kim et al. measured ultraviolet radiation passing through different types of automotive glass using calibrated UV detection instruments. The study compared front windshields with side windows across multiple vehicles and assessed both UVA and UVB attenuation (Kim et al., 2024).

The findings showed that front windshields provided near-complete attenuation of UVB and substantially reduced UVA transmission, with attenuation approaching 99 percent. In contrast, driver-side windows allowed significantly higher levels of UVA to pass through, resulting in measurable UVA exposure inside the vehicle. The differences in UVA transmission between windshield and side window glass were statistically significant, indicating that window type materially influences cumulative exposure (Kim et al., 2024).

These results demonstrate that while vehicles effectively reduce sunburn-associated UVB exposure, they do not fully eliminate UVA exposure, particularly during prolonged driving. This distinction is relevant when considering long-duration, low-intensity exposure scenarios where UVA is the dominant contributor to cumulative dose.

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 and reduces reliance on repeated reapplication in low-intensity environments.

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

Kim, J. H., Lee, S. Y., Park, H. J., & Cho, S. (2024). Measurement of ultraviolet radiation transmission through automobile glass and implications for cumulative exposure. Photodermatology, Photoimmunology & Photomedicine, 40(1), 45–52. https://doi.org/10.1111/phpp.12915

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