Question: when are babies no longer obligate nose breathers

title: Obligate nasal breathing
text: Human infants are commonly described as obligate nasal breathers as they prefer breathing through their nose rather than mouth . Most infants , however , are able to breathe through their mouth if their nose is blocked . There are however certain infants with conditions such as choanal atresia in which deaths have resulted from nasal obstruction . In these cases there are cyclical periods of cyanosis . The infant initially attempts to breathe through the nose , and is unable to ; hypercapnia occurs , and many babies instinctively begin to cry . While crying , oral ventilation occurs and cyanosis subsides . There is variation in the length of time until a baby begins oral breathing , and some will never cease attempts at nasal breathing . It has also been suggested that infants may not be able to sustain oral breathing for significant lengths of time , because of the weakness of the muscles required to seal the nasal airway and open the oral airway . 

Answer: answer: Most infants are able to breathe through their mouth if their nose is blocked . There is variation in the length of time until a baby begins oral breathing , and some will never cease attempts at nasal breathing . It has also been suggested that infants may not be able to sustain oral breathing for significant lengths of time , because of the weakness of the muscles required to seal the nasal airway and open the oral airway .