Humans produce more oil on the surface of their skin than our closest relatives (1). Oil is used by the majority of organisms to store energy and it is metabolically expensive to produce … yet we secrete around 14g a day. That’s worth 132 calories per day, which is around 7% of our daily metabolic output. Surely evolution wouldn’t favor a human that needed to eat more to produce an oil on its skin unless that oil was doing something important?
Evolution may not be perfect but its solutions to life on earth are usually elegant and efficient. It is becoming increasingly clear that we produce sebum in order to maintain barrier function and feed the multitude of microbes that live on our skin. We do this in exchange for the protection afforded us by our skin microbiome.
In the last 100 years advertising campaigns have convinced us to use soap and warm water to wash our natural oils and our surface microbiome down the drain every day. This forces skin to produce more (lower quality) oil in an effort to keep up.
To make things worse, we try to replace sebum with other oils (often petrochemicals). The oil produced by your skin is complex and unique to humans. Trying to mimic it is like trying to copy breast milk … almost impossible. Why not just leave this highly curated oil on the skin surface … like we have for the last 300 thousand years?
As a bonus we might have a bit more energy?
(1) DONALD T. DOWNING et al, THE JOURNAL OF INVESTIGATIVE DERMATOLOGY, 77:358-360, 1981