Skin oil does not provide any UV blocking. The oil in sunscreen is to make it spreadable and dilute the UV-absorbing ingredients, which are things like avobenz

Skin oil does not provide any UV blocking. The oil in sunscreen is to make it spreadable and dilute the UV-absorbing ingredients, which are things like avobenzone, oxybenzone, and so on. No offense, but you could have googled "active ingredients in sunscreen." Further: just because something is called an "oil" doesn't mean it has any similar physical properties compared to another oil. Recipes for soap date back something like 5,000 years, by the way - and probably were passed down by oral history or demonstration even earlier. You don't seem qualified to be making (or evaluating) the theories you are coming up with. Not in terms of basic scientific knowledge, critical thinking skills, or research skills. Your "people didn't wash back then so they had natural sunscreen" is about as well-reasoned as the people who think keto is the best diet because "it's what cavemen ate" (hint: people ate whatever was available to them in their area.)