Topic Of Religion- Hygiene And Health
After reading this link https://www.preceptaustin.org/leviticus_1_commentary#Leviticus%20Commentary I can say that Initial chapters of leviticus are devoted to rules and regulation to be observed for offering prayer. Hence these guidelines. I think it is analogous performing wudu or ghusal verse in Quran. (thats my opinion i may be wrong)
It seems covering the lower part of the face eg the mouth and nose was specifically to keep diseases away.