Hello. What could cause cheeks to blush? We're on an IV, but I don't t…

Hello. What could cause cheeks to blush? We're on an IV, but I don't think it's due to the formula. Since we haven't changed the formula, and the cheeks either blush or are normal, they go away by themselves, except for baby cream with a series of not something else to apply. Breastfeeding has not been introduced yet... Could it be on the teeth?