We all know we should wear sunscreen. Whether or not we do -- or do so correctly -- is a horse of a different color.

But skin cancer remains the most common form of cancer in the U.S., and more than 9,000 people died from aggressive skin cancers in 2010, the most recent year from which data is available, according to the CDC, and a history of sunburns significantly increases the risk.

With early detection, many new cases are highly treatable, but some skin cancers are also highly preventable, especially if we stop ignoring the problematic areas we so often skip in our sunscreen routines. Here are just a few of those pesky parts. Let us know in the comments what we missed.

Ears
According to a 2007 study from The Skin Cancer Foundation Journal, the ears are the third most frequent location for basal cell carcinomas , which make up about 80 percent of the 1.3 million new cases of non-melanoma (less-aggressive) skin cancer in the U.S. each year, according to the University of California, San Francisco School of Medicine.

Scalp

You might not even realize until you run a comb through your hair the next day that you completely missed your part. Ouch.

Eyelids
You forget 'em under those huge shades, but then you take your shades off to avoid funky tan lines. Protect that very-gentle skin! Because getting your sunscreen in your eyes is almost as much fun as getting a sunburn, Consumer Reports recommends using a moisturizer or eye cream that contains SPF , since those are absorbed more easily. Just be sure to reapply if the SPF count is low.

That Pesky Armpit Skin

First thing's first, can we give this little jiggle of skin an official name? It's easy to miss, scrunched there next to your strap, but you won't be happy about it if you do.

Under Those Straps
Speaking of straps! Unless you're wearing a UV-blocking swimsuit, you can get burned through the fabric . Plus, if you only apply around the straps, even the slightest movement can expose unprotected skin. That's at least part of the reason why some experts recommend putting on your sun protection while you're in the buff , so you can't miss a single strap-covered spot.

Tops Of Feet

People. Your flip flops are the bikini straps of your feet. Cover up!

Backs Of Hands
Yes, we know, you wash your hands after you're done applying sunscreen because, well, ick. But in the process, you're also leaving your hands woefully unprotected. The palms of our hands (and soles of our feet, for that matter) are protected by a thick layer of dead skin cells that limits the amount of UV light that can get in . The backs of our hands are in no such luck, Popular Science reported.

Lips

The lower lip in particular needs some sunscreen love, as it's 12 times more likely to develop cancer than the top lip , according to the SKin Cancer Foundation. And men, don't shy away from lip balm: You're up to 13 times more likely to develop lip cancer than women.

Back Of Knees
They're in no-man's-land -- not quite lower leg, not quite upper leg -- and we can't see 'em. Whatever the reason we neglect our knee pits, forget this crucial crease and you'll never want to walk or sit again.