Damage from what? The environment! We are talking about high energy beyond what our skin can cope with. There will be energy from ultraviolet radiation that damages macromolecules (like DNA) directly plus the reactive oxygen species (ROS*) formed when the UV reaches the skin and reacts with molecules capable of producing those. These UV-produced ROS* add up to those present in the air.
Yes, our skin has evolved beautiful mechanisms to defend us from those dangers but evolution did not prepare us for suntans or for city pollution.
Read more about ROS*, sun, and their effect on our skin in my book and in this blog. For example:
DISCLAIMER: These claims have not been evaluated by the FDA and are not intended to diagnose, cure, treat or prevent any disease.