Clouds, water, glass: surprising things that solar UV can pass through

First published 27 June 2017, revised 20 May 2025

Do you know that over 90% of UV can pass through light cloud, at half a metre depth under water UV is still 40% as intense as it is at the surface, and some UV can pass through glass!

We’re all becoming more aware of the importance of protecting ourselves against overexposure to ultraviolet radiation (UV) from the sun when outdoors but you may be surprised to know that chronic exposure of the skin to UV over many years in some ‘indoor’ settings e.g. through window glass or when driving, can cause ‘invisible’ skin damage, resulting in premature skin ageing and may increase skin cancer risk.

Solar UV

UV from the sun is divided into three categories, classified according to wavelength: UVA, UVB and UVC. As sunlight travels through the Earth’s atmosphere, all UVC and most (90% or more) of UVB is absorbed, while UVA passes through relatively unchanged. Therefore, two types of UV radiation are of concern: UVA and UVB.

UVA & UVB

Longer wavelength UVA rays penetrate more deeply through the layers of the skin than shorter wavelength UVB. UVA is mostly involved in skin ageing while UVB is mainly responsible for sunburn. However, both types of UV are linked to the development of skin cancer.

UV damage

Skin varies in susceptibility to damage from UV, depending on factors like individual level of pigmentation (natural skin colour) and how the skin reacts to sunlight (whether it burns easily or tans). People with light skin pigmentation are comparatively more vulnerable to UV damage than those with darker skin pigmentation.

Car and windscreen glass

While UVB does not pass through window glass, UVA may be transmitted, depending on the type of glass. For example, for safety reasons in cars, windscreens are made from laminated glass which holds together better if broken. Laminated glass also provides an effective shield against UVA. However, side and rear windows may not be laminated, so a higher proportion of UVA can pass through.

More UV damage on the driver’s side

Some interesting studies have shown that premature skin ageing, skin damage and skin cancers are more common on the side of the driver’s body (e.g. face, neck, arm) next to the window, i.e. the left side in America and the right side in Australia. Driver’s UV exposure may be as much as ‘20- fold stronger’ on the arm closest to the window. It is thought that cumulative UVA exposure through window glass over many years may play a role in skin cancer development.

Vehicles, glass greenhouses and windows…

The extent to which glass provides UV protection depends on a variety of factors such as glass type, colour, coatings etc. But other ‘non-glass-related factors’ can also influence UVA exposure e.g. a person’s position in a vehicle, their direction of travel in relation to the sun and time of day. So, for example, those who spend long periods driving, sitting next to a window or working in glass greenhouses may wish to consider their personal circumstances and taking UV protective measures to reduce their cumulative UVA exposure through glass.

Some recent articles/further reading:

Axelson GE, Constanza J, Rezaee R, Axelson A, Cenci A, Khan A, Weimann R, Ilyas EN. Evaluation of UV-A and UV-B transmission through the windows of gas, hybrid, and electric vehicles. Archives of Dermatological Research 2025; 317: 294
Chowdhury M, Abir Ahsan TM, Ahamed M. Assessment of health hazards of greenhouse workers considering UV exposure and thermal comfort. Smart Agricultural Technology 5 (2023) 100319

Next article: Being SunSmart: At a glance