[PancakeBrah]

Maybe facial hair, since it could affect the perception of a smile or the machinations of your face when you emote.

To be honest, this isn't scientific, just based off personal experience. I went through long hair stages and buzz cut stages and it didn't affect anything at the present or in the long term. I vaguely remember reading one of those baby books and reading that the most important factor is the sense of care the child associates with you and actual facial expression. Hair seems superfluous.