Different forms of skin cancer occur for different reasons. For example, with nonmelanoma skin cancer, repeated sun exposure leads to cumulative changes in the DNA. DNA is essentially the instruction manual your body follows when it makes new cells. When the sun’s harmful rays zap that DNA over and over, it’s a lot like what happens when you accidentally spill your coffee on a notebook with fresh ink on it. Just as the ink on those pages can start bleeding and blurring, the DNA changes and starts making cells incorrectly.