The fascinating reason why newborn babies don't cry tears.

Newborn babies cry a lot. We know this. But unless you’ve been up close with a screaming, little – erm – angel, you may not have realised that they don’t actually produce any tears.

Truly. No matter how upset they are, their cherubic cheeks stay as dry as their nappies… aren’t.

So why is it that newborns don’t turn on the waterworks? And at what point does that change?

We asked Dr Phillipa Sharwood, a Brisbane-based paediatric ophthalmologist and member of the Royal Australian and New Zealand College of Ophthalmologists, to explain.

Why don’t newborn babies cry tears?

It’s all to do with the tear glands. Formally known as lacrimal glands, these small, almond-shaped organs sit underneath the top eyelid, above the eyeball, and are responsible for tear production.

“It’s almost like the cloud that makes it rain. The tears then come down over the eye, and there’s a drainage system (the tear duct) in the inside corner of the eye that goes down into the nose,” Dr Sharwood told Mamamia.

“How much we actually cry – as in how much spills down our cheek – depends on how good the drainage system is, versus how much tears the glands produce.”

In the case of newborns, Dr Sharwood explained, that production is limited: “Babies don’t produce a normal amount of tears when they’re born, because their tear glands aren’t completely developed yet.”

Does that mean newborns' eyes are dry or irritated?

No, they shouldn't be.

"We have a few different different types of tears," she said. "There's a baseline level that keeps the eyes moist and healthy, and [newborns] have that.

"The next is reflex tears, which are the tears that form when you get something in your eye, or you sneeze or cough. They start to develop that in the first few weeks after birth.

"Then there's emotional tears."

That's where newborns fall short. Emotionally triggered tears are produced at a higher volume, and their still-developing tear glands simply don't have the output yet.

When do babies start crying tears?

"Babies don't produce enough from their tear glands to get full emotional tears, usually, until at least a couple of months after birth," she said. "But that does vary. Some take just a month, others take even up to six months."

She notes that there are a very small number of people who never develop proper tear production, but stresses that such cases are incredibly rare.

"As long as a child has nice, white, comfortable eyes, we wouldn't be too worried," she said.

If you have any concerns about your baby or child's eye health, please consult your doctor.