Epidermis is the outer layer of your skin, the part you can actually see and touch. It's like a protective wrapper covering your entire body, shielding what's underneath from dirt, germs, and injury.

The epidermis is remarkably thin, about as thick as a sheet of paper on most of your body, though it's thicker on the palms of your hands and soles of your feet where you need extra protection. Despite being so thin, it's surprisingly tough and constantly renewing itself. The cells on the very surface are actually dead, creating a tough barrier, while living cells underneath keep dividing to replace them. You shed millions of these dead skin cells every day, which is why dust in your house is partly made of old epidermis.

The dermis is the thicker layer beneath the epidermis that contains blood vessels, nerve endings, and hair roots.

When you get a shallow scrape that doesn't bleed, you've only damaged the epidermis. If it bleeds, you've gone deeper into the dermis.