Why hasnt anyone managed to invent a true sunless tan( not like skin dyes)?

Okay so sun can give you cancer, tans protect you from sun damage but to get a tan you have to get skin damage. Fake spray on tans or other methods of fake tans dont actually tan you but just tint the skin with a dye. Why havent they created something to just simply activate the tanning process without the damage done to the skin?