Myth busted: You can't get burnt on a cloudy day

UV radiation is energy produced by the sun. The two types that reach the earth’s surface are UVA and UVB.

UVB is the primary cause of sunburn, while UVA can penetrate more deeply into the skin and contributes to premature skin ageing and long-term skin damage. Both types of UV radiation can damage skin cells and contribute to the development of skin cancer.

Unlike heat, UV radiation doesn’t disappear when the temperature drops or clouds move in. Some UV can still pass through cloud cover and reach your skin. This means you can be exposed to enough UV to cause sunburn, even when the day feels cool or the sun is hidden.

The Cancer Society of New Zealand explains that UV radiation cannot be seen or felt. The warmth we feel from the sun is caused by infrared radiation, not UV. This is why the temperature is not a reliable guide to how much UV exposure you are receiving. (Cancer Society of New Zealand)

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On a hot, sunny day, we are more likely to think about sun protection. We may reach for a hat, apply sunscreen or look for shade because we can feel the heat on our skin.

Cloudy days are different. The cooler temperature can makeit difficult to recognise that UV levels may still be high. You might spendlonger outside because the weather feels comfortable, or skip sunscreen becausethe sun is not visibly shining. This can result in significant UV exposurebefore you realise it.

UV exposure can also happen during everyday activities, including walking the dog, gardening, watching sport, commuting or eating lunch outdoors. You don’t need to be deliberately sunbaking to experience enough UV exposure to damage your skin.

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The best way to decide whether you need sun protection is to check the UV Index, rather than relying on how warm or sunny it feels.

The UV Index measures the strength of sunburn-causing UV radiation at the earth’s surface. In New Zealand, sun protection is recommended when the UV Index is 3 or above, regardless of whether the day is sunny, cloudy, cool or windy.

NIWA describes a UV Index below 3 as low. When the UV Index is above 3, sun protection is recommended to help reduce the risk of sunburn and skin damage. (NIWA –UV and ozone)

You can check the UV Index and local UV forecasts through NIWA’s UV forecasts or your preferred weather app.

Cloudy or not, make sun protection part of your daily routine when the UV Index is 3 or above. Slip on protective clothing, slop on SPF50+ sunscreen, slap on a broad-brimmed hat, seek shade and slide on sunglasses. The clouds may hide the sun, but checking the UV Index helps ensure your skin isn’t left unprotected.