At this the time of year the sun is at its highest and the risk of sunburn is at its greatest. Despite all the publicity about covering up and using sunblock, it's still surprisingly easy to underestimate the power of the ultraviolet (UV) rays in sunlight that cause both sunburn and skin cancer.
Clouds can often give a false sense of security. A thick blanket of cloud covering the sun filters out a large part of the UV, but thin or broken cloud cover can allow much more UV through. Worse still, a patchwork of clouds near the Sun can actually increase the UV levels on the ground by reflecting more of the rays, rather like giant mirrors.
Another myth is that glass protects against UV, but this isn't always true. Two recent surveys of the incidence of skin cancer in the US revealed a puzzling discrepancy, with many of the cancers only occurring on the left hand side of the body, particularly on the face, arms and hands, and this tended to be particularly striking in men.
The studies revealed that these people had spent a lot of time driving, and in the left-hand drive vehicles the drivers are exposed to UVA rays that can often penetrate through the side windows of their vehicles. Although laminated windscreens tend to filter out UV, the side and rear windows are usually made of clear, non-laminated glass that filters out UVB but still allows UVA rays to penetrate, and this contributes to skin cancer.