Today is to remind us that our sun is dangerous so we must protect ourselves. Of course, we need the sunlight as our main source of Vitamin D, which keeps out bones healthy. However, the UV rays aren't so good.
With my ridiculously pale, Northern European skin, I can burn without trying. Five minuted outside is enough to turn my exposed skin red. As a result, I use sun screen with an SPF of 50. Even then I can't stay out too long.