Which of the sun's rays actually cause skin cancer?

It is mainly the ultra violet rays, UVA and UVB which cause the damage. UVA rays penetrate deep into the skin, gradually destroying elasticity and causing premature ageing. UVB rays cause skin damage and can alter the structure of skin cells, and ultimately lead to possible skin cancer. UVC rays are the most dangerous but as they are blocked out by the ozone layer, they don't reach the earth's surface. A broad spectrum, SPF30+ sunscreen will help protect against UVA and UVB radiation.