When is the last time you spent a day at the beach? Unless you live in sunny Southern California or were lucky enough to vacation somewhere warm recently, it's probably been a while since you soaked up any sun. Does that mean your sunscreen has been sitting on a shelf untouched? Tsk tsk! You should be using SPF year round on any uncovered areas of skin. "While ultraviolet B (UVB), the sunburn rays, are weaker during the winter months, ultraviolet A (UVA) radiation, which can lead to photoaging and skin cancers, is constant throughout the year. For this reason, it is important to include sun protection as daily ritual year round," says Nelson Novick, M.D., Clinical Professor of Dermatology at the Mount Sinai School of Medicine, NY. In case you need further proof of the importance of wearing sunscreen in the winter, keep reading for the top five reasons to start slathering your skin with the stuff today.

1. Skin burns regardless of the temperature

It may be cold outside, but that shouldn't lull you into thinking you can't get sunburned. The sun is actually closer to the Earth during winter and its rays are just as harmful now as they are in summer. If you plan on spending more than 15 minutes outside, be sure to coat any exposed skin with sunscreen that has an SPF of at least 15.

2. Snow makes the sun's rays stronger

While you're shooshing down the slopes, all that powder is reflecting 80 percent of the sun's UV rays right back at your skin. The effects are similar to a day at the beach. Whenever you're around snow or ice—say, snowboarding, ice skating or cross country skiing—be sure to wear a sunscreen with an SPF of at least 30, just like you would for an afternoon of sun and sand in the summer.

3. Makeup with an SPF is not enough

Dermatologists agree that you're probably not applying enough of that protective foundation or tinted moisturizer to truly keep your complexion safe from the sun. To guard against sunburns and many common signs of aging, first apply a lotion with broad spectrum protection, wait five minutes for it to be completely absorbed, then apply makeup as usual.

4. Sunburn and windburn look and feel the same

It's easy to confuse the symptoms of sunburn and windburn: both cause reddening on the face in areas where the sun naturally hits (the cheeks, nose and forehead) and both leave your skin with a sting. The difference is that you can prevent sunburn by wearing adequate sun protection during the winter.

5. The sun is stronger at higher altitudes

UV intensity increases by 10 percent for every 1,000-foot increase in elevation. That means your skin is more susceptible to the sun's burning and aging rays when you're enjoying winter activities like skiing and snowboarding, so staying protected on the slopes should be a priority.

Megan O'Neill is Beauty Editor at EndlessBeauty.com.