Cold exposure on the face, such as sleeping in a cool room, can activate brown fat due to high density of cold receptors.

“Studies have shown — that if you just put your hand in cold water not that you're going to going to do that all day or or every day or anything it's not it's it's not something you have to do but it just just shows that you can activate your brown fat just by getting a temperature change on your skin so you can go outside and t-shirt”

“so it's you have so many co-receptors in your face so it's actually it's enough and it I think corresponds very well with the studies showing that you can activate the brown fat just by putting a hand into a bucket of cold water”