Boys nose is big for the following reasons: 1, the male nose is usually bigger than girls, because the male body type especially after puberty, usually bigger than women, the face is also big, the nasal structure in the whole face structure has a certain proportion, the male due to the face is bigger than the girls, so the shape of the nasal cavity than the girls to be big; 2, depending on the male physical fitness and basal metabolic rate, males, especially after puberty, exercise, muscular demand, basal metabolic rate are higher than women, oxygen demand is very large. Nasal cavity mainly has the function of absorbing oxygen, in the process of exercise or the usual basic metabolic rate needs more oxygen, then the shape of the nasal cavity or nostrils, nasal cavity need to increase accordingly.