Tanning is a natural process. Your body is designed to produce melanin, which darkens the skin. A tan is your body's natural way of protecting you from sunburn; for most people a base tan can be equivalent to an SPF 4, meaning you can be exposed to UV light 4 times longer than without a base tan. It's what your body is designed to do. Sunburns are a totally different process.
Sunburn is an injury to the skin; the red color is actually increased blood flow, which is sent to the surface of the skin to help your body repair the damage done by overexposure to ultraviolet light. If you sunburn, this actually slows down the tanning process as your skin now has to repair itself before tanning.
Think of it like this… Imagine pouring a glass of water and it overflows. Now you have to clean up that spill before taking a drink of your water. You must be patient while building up a base tan as this process takes time. It doesn't happen in just one session. It can take a couple of weeks to build a good base tan. Your skin type also plays an important role in how your skin can tan. Everything in moderation is smart tanning. Never sunburn!
Smart Tanning Means Wearing Protective Eye Wear
Your eyes do not tan. Eye damage may occur without the proper use of FDA-approved eye protection. Make sure that your eyewear creates a light-tight seal around your eyes. By tanning without your eyewear you increase your risk of cataracts, loss of night vision, loss of distinction between colors and even increase your vision loss.
UV light penetrates about 2-3 mm into your skin and your eyelids are not this thick so just closing your eyes or putting a towel over your face is just not enough. Be wise and protect your eyes.