We all know that a key ingredient of healthy skin is sunscreen. After all, 90 percent of the signs of aging-fine lines, wrinkles, and brown spots-are caused by the sun. But healthy skin doesn't stop there. You need to keep watch over all the spots on your body to be sure they're not cancerous moles.

How bad can a mole be? One in five Americans will develop skin cancer over the course of their lifetime and melanoma is the most common form of cancer for young adults 25 to 29 years old. Unfortunately, about 68,720 melanomas will be diagnosed this year, with nearly 8,650 resulting in death. That's serious.

The good news is that 99 percent of patients whose melanoma is detected early-before it's penetrated the epidermis-survive. The key to early detection is knowing how to spot cancerous moles.

Find out how to spot cancerous moles with our simple mole guide. The images on the top are benign, non-cancerous moles and those on the bottom are malignant, cancerous moles. Make an appointment with your doctor immediately if you see a mole with any malignant characteristics. Prepare yourself: These photos aren't pretty. But they may save your life.