Skincare 101

The scoop on the UV Index

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Swan Sunburn

quick advice

If your shadow is shorter than you are (around midday), you are being exposed to higher levels of UV radiation.

Amidst all the mortgage ads and clickbait, you see it almost every time you pull up your forecast – the UV index. But what does the number actually mean?

What is the UV Index?

The UV Index provides a forecast of the expected risk of overexposure to UV radiation from the sun, and it’s expressed on a scale of 0 (low) – 11 (extremely high).  

UV Index

(Just when you thought red = greatest danger and scales were from 1 to 10, purple at 11 is all out insanity.)

How is it calculated?

The U.S. National Weather Service uses a fancy computer model that relates the ground-level strength of solar ultraviolet (UV) radiation to forecasted ozone layer strength, forecasted cloud cover, location elevation, and general ground observations. If you really want to geek out on it, see the detailed calculation method here.

What is the UV Index today?

Take a guess before you click here. Hint – this time of year, it’s high just about everywhere in the US.

What’s the Shadow Rule and what else do I need to know?

An easy way to tell how much UV exposure you’re getting is to look for your shadow. If your shadow is taller than you are (in the early morning and late afternoon), your UV exposure is likely to be lower. If your shadow is shorter than you are (around midday), you are being exposed to higher levels of UV radiation. The shorter the shadow, the higher the UV exposure. Protect your eyes with some quality shades and liberally apply sunscreen of SPF 30 or greater! Remember that chemical based sunscreens take 20 – 30 minutes to truly start protecting you, so make sure you apply before you head out the door.

How do UV rays affect my health?

Most of you know this, but in short, nothing good comes of it. Skin cancer is the big one – unfortunately there are now more new cases of skin cancer are diagnosed in the U.S. than new cases of breast, prostate, lung, and colon cancer combined. And one in five Americans will develop skin cancer in their lifetime.

UV exposure and time in the sun also contributes to premature aging. While part of this is certainly natural and comes with living and enjoying life, up to 90 percent of the visible skin changes commonly attributed to aging (fine lines, wrinkles, age spots, etc.) are caused by the sun.

How can we protect ourselves?

The good news is that unprotected exposure to UV radiation is the most preventable risk factor for skin cancer, so we can act on this today. Keep applying your sunscreen daily and your skin will thank you in the weeks and years to come. Our best advice? Don't worry about the UV index number in terms of sunscreen application. Know that during the heat of the summer day, especially if you're outside, reapply liberally. And on cloudier days (or in less sunny seasons), know that UV rays still make it through clouds to cause those fine lines and wrinkles none of us want.

When the UV Index is low in non-summer seasons, should I still wear daily sunscreen?

Absolutely, and of the broad spectrum variety. Why? We might not get as sunburned or tan during winter (caused by UVB rays; think 'B' for burning), but UVA rays still exist and penetrate clouds and windows (think 'A' for aging). Set it and forget it, we say.

For more on sun protection, read our summer roundup on all you need to know about sunscreen.

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