12 July 1998
Cancer-Causing UV Light Worms Its Way Into The Shade
Just because you've forsaken the hot summer sun for the shady sanctuary of the nearest tree, don't think you can neglect your Factor 15. For as researchers at Purdue University and the US Forest Service have discovered, cancer-causing ultraviolet-B (UVB) light can infiltrate even the coolest of shade. And since you can't see it, you'd be none the wiser.
Unlike visible light which shines directly down from the sun, UVB bounces around the atmosphere - snaking its way under beach umbrellas and trees alike.
Says researcher Richard Grant from Purdue: "When people in the shade estimate UVB exposure based on eyeball assessment, they're getting about twice as much UVB as they think.
"How much UVB you're getting more closely correlates with how much sky you can see. If lots of the sky is obstructed, you're getting a lot less UVB." Which means you're better off surrounded by tall walls without a hint of shade than you are under a solitary tree in a field.
Grant teamed up with the US Forest Service's Gordon Heisler after noticing that articles in the popular press have generally urged people to seek refuge in the shade to avoid ultraviolet exposure. Taking measurements of UVB along tree-lined streets, in farm fields and in grassy areas away from streets, the duo proved that such advice may be less than helpful for avoiding skin cancer and an impaired immune system.