[caymanjim]

Keeping a "local air layer" near your skin is not going to help at all with summer cooling. You need constant sweat evaporation to cool off. I don't think a beard is going to have much effect either way, since it's small, and our cheeks and chins are not designed to radiate heat or even sweat much compared to most of the body.

[pbhjpbhj]

Surely if the evaporation can cool the skin surface, then a local insulation layer would prevent ambient air from heating the skin. Just as a locally warmed layer prevents ambient air from cooling the skin during Winter.

It's certainly a hypothesis I've long held but never had chance to test.

Citations for support/contradiction welcome, thanks.

[caymanjim]

Unless it's above body temperature, the local ambient air isn't heating your skin up, and if it's that hot you need to sweat profusely to avoid hyperthermia.