Skin discoloration?

Hi my baby is 1 month 24 days.. near her mouth there seems to be a fairer shade.. but when i stretch her skin out.. it doesnt seem to have a really round spot of white skin shade.. not sure is it because of phototheraphy and her skin is becoming fairer again or what? Any mummies encounter this? It doesnt look like fungal or rash... havent brought her out to the sun too.. so i dont think its cause of the heat.. hoping to find answers! Thank u.