Sunscreen only works if you're actually wearing it. And it's too easy to go through the motions of putting on sunscreen while still leaving large amounts of skin unprotected. Even if you're applying the recommended shot glass of sunscreen before you head out into the world, parts of your skin may still be exposed to harmful rays. Just check out these UV images taken by researchers at the University of Liverpool, spotted by the UK's Metro.

The black-and-white images were taken with a UV camera so that any part of the skin covered by UV-blocking sunscreen would appear dark. Skin without sunscreen on it, by contrast, remains visible. The 57 volunteers in the study—which was recently presented at the British Association of Dermatologists' Annual Conference—were instructed to apply sunscreen to their face as usual.

Some volunteers were more thorough than others, but as a whole, the group ended up missing a median of 9.5 percent of their faces. Men with beards tended to miss a lot of their faces, you might notice in the photos, and people seemed to have trouble with covering the full area around their mouth. However, the main problems occurred around the eyes. Many people missed their eyelids, and more than three-quarters of the group missed the medial canthal region, or the area between the bridge of the nose and the inner corner of the eye.

The finding is significant because the area around the eyes are particularly susceptible to skin cancer. According to the abstract presented at the conference, 5 to 10 percent of skin cancers occur on the eyelids.

Knowing this doesn't necessarily help, though. When the participants were brought back for a second visit, the researchers gave them new instructions that included data on cancer risks for eyelids, the results barely changed. People put slightly more sunscreen on around their eyelids (they missed a median 7.7 percent instead of 13.5 percent of the area) but almost everyone still missed their medial canthal area.

It's not a surprising finding, considering the fact that no one wants to get sunscreen in their eyes. Sunscreen manufacturers recommend that you keep it out of your eyes, and if it does run, you'll end up in tears. So it's not particularly useful to tell people they should be coating their eyelids in Coppertone.

To keep your face super smooth and reduce your likelihood of sun damage, then, the message is clear. Better get some shades, unless you've got a UV-blocking eyeshadow on hand. Better yet, get yourself a hat, too.

[h/t Metro]

All images by Kareem Hassanin, courtesy Kevin Hamill