How to relieve red-brown, flaking skin under the mouth?

Yeast rash: One of the conditions that can cause some flaking and scaling on the chin area is "seborrheic dermatitis" this is a common yeast overgrowth problem and is worsened by stress, anxiety and some other triggers. Try some head & shoulders shampoo as a face wash three times a week, leave on 30 seconds. If this doesn't clear is up in a couple weeks, follow up with a dermatologist or your primary.