Unlike the rest of your skin, your lips have an extremely thin outer layer. This lets moisture evaporate more quickly. Your lips also have none or just a little melanin. Melanin is the natural pigment that screens out the sun. Lips also have few sebaceous glands and make little natural oil. And finally, lips are almost always exposed to the elements.

Lipstick and lip gloss do provide some protection. But they can't give you the same protection as a product made with an SPF rating. Don't lick your lips, because saliva acts like a lens and makes the sun exposure stronger.

Collagen gives lips body and resilience. It can be altered over time. Fine lines and wrinkles can develop as well. Prevention is the best defense to keep your lips healthy. That's because it can take years to see the effects of overexposure. Sun exposure can actually trigger an outbreak of cold sores, not clear them up. Lips will not tan, because they have little or no melanin.

It's important to protect your lips from the sun at all times. The level of UVB rays—those that contribute most to skin cancer—is greater in warmer months. But the level of harmful UVA rays throughout the year is fairly constant. Clouds don't protect you from UVB rays. Snow reflects the sun's rays, which increases your risk for sunburn.

Over time, too much sun exposure can cause skin cancer to develop. Sun exposure can also trigger cold sores or cheilitis. Cheilitis is an inflammation of the lips.

Sensitivities or true allergies to certain types of food, makeup, or cigarette smoke can develop at any time. Wearing lip balm can't prevent an allergic reaction. But dry lips are more likely to get irritated.

Lips need more moisturizing and conditioning as you age. The outer layer of skin thins even more, and natural hydration decreases.