In Australia, they recommend sun protection when the UV index is above 3. Why is this? Surely whenever it's above 0 there are still UV rays hitting your skin? Would 10 minutes in the sun with a UV index of 6 be the same as 20 minutes in the sun with a UV index of 3? If so, surely 10 minutes in a UV 6 index would be bad, and therefore 20 minutes in UV index 3 would also be bad?