Question

It important to avoid tanning salons and wear a hat, sunglasses, and protective clothing whenever you spend time outside because they protect you from excessive exposure to ________, which causes melanoma and other types of skin cancer.

Answer 1

To uv rays is your answer. ;)

Answer 2

It important to avoid tanning salons and wear a hat, sunglasses, and protective clothing whenever you spend time outside because they protect you fromexcessive exposure to ultraviolet rays  which causes melanoma and other types of skin cancer. 
Hope I helped, and good luck!