You’ve got sunshine on a cloudy day.
Studies show UV damage can be worse when it’s overcast out there.
Just because it’s cloudy and cold outside, that’s no reason to forget your sun protection routine. Studies now show that cloudy skies with low temperatures actually result in more extreme UVB exposure and damage than on clear sunny days, under “the right conditions”.
When UVB gets really bad.
As regular readers of this blog will know, UV comes in two flavours – UVA (more common) and UVB (more damaging). Each can play a part in skin cancer and eye damage, but UVB is directly responsible for nastier forms of sunburn – on your skin and in your retinas.
You need to get some daily UVB to produce vitamin D, which keeps you happy and energised. But experts agree that it’s best to protect yourself from it when the UV rating reaches 3 out of 20 – and this can occur even when the sun doesn’t seem to be shining in your neck of the woods.
A case in point – as I write it’s completely overcast outside my window. But when I visit the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) website to see UV levels in real time I see that, despite the clouds, Melbourne will experience damaging UVB levels from around midday, today.
This is because UV radiation can penetrate through thin cloud, creating high UV readings at ground level even when it’s overcast.
The really scary part is that most UV indexes don’t even factor in the effects of reflective cloud cover, so the UV levels may be even worse than appear to be estimated.
Rule of thumb: broken clouds = extreme UV levels.
Patchy clouds are even worse for UVB. They intensify UV levels because radiation is often reflected off the edges of the clouds, creating a mirror effect.
So, if you see patchy cloud, be careful. At the ground, UVB levels can be extreme.
Scientists call this the “broken cloud effect.” While on a really overcast day clouds can stop 70 to 90% of UVB from reaching the surface, something interesting happens when they start to break up.
According to a 1994 survey conducted in six US cites, cumulus clouds can raise surface UVB by 25%. Additionally, in 2004, Australian researchers reported that the UVB rays associated with DNA damage were up to 40% stronger under partly cloudy skies.
As well as extra reflection bouncing off dense clouds, UV rays can be redirected when they pass through wispy clouds, reports an American Scientist article. Apparently the combination of these wispy and dense clouds also results in a significant UV boost at the earth’s surface.
Haze and pollution don’t help either. Both redistribute UV radiation, scattering UVB and effectively turning the entire sky into a source of radiation. So standing in the shade with a hazy sky above can expose you to a great deal more UVB than if you were out in the open on a clear sunny day!
Bottom line: Take precautions whatever the weather.
Your eyes are your only internal organs directly exposed to the sun, so they’re particularly susceptible to UVA and UVB damage.
We’ve absorbed a lot of important warnings about UVB and skin cancer over the last 20 odd years – slip, slop, slap is pretty well ingrained in our psyches. But the problem with UVA and UVB damage to your eyes is that you just don’t know how much is “too much” until it’s too late.
Don’t play Russian roulette with your eyesight, folks. It’s too precious. Wear your sunglasses even on cloudy days, just to be on the safe side.