新生儿刚出生时既不会produce泪水也不能生成口水，除非满屋子大蒜的刺鼻气味～～～
Newborn Babies Will Cry Without Tears Until They are Several Weeks Old
Newborn babies are incapable of producing actual tears because their tear ducts haven’t fully formed yet. In many cases, their underdeveloped tear ducts can also be clogged with amniotic fluid for a time after birth.
Every baby is born with basal tearing, which means that their tear ducts create enough moisture only to keep the eyes wet and healthy. Proper tears in a baby begin around 3 to 12 weeks old. In some cases, it will take even longer – up to the first several months of a baby’s life.
Interestingly, despite this lack of “crying” tears, newborns do have reflex tearing; the kind that adults get when slicing an onion, for example.
Bonus Factoid:
Babies are also born without fully functioning salivary (spit) glands. At first, their food is entirely liquid so there is no need for saliva. During the first three months of baby’s life, their salivary glands kick into gear and another problem appears – swallowing your own saliva is a learned skill which a baby hasn’t developed yet, which is one of the reasons babies tend to have a bit of a drooling problem.
