You’ve probably tasted your own tears and figured they have salt in them. What you might not realize is that tears contain a lot more than just that — and that they serve some very diverse purposes!

Let’s take a look at what tears are, how they work, and some surprising facts.

Your tears have a similar structure to saliva. They’re mostly made of water, but also contain salt, fatty oils, and over 1,500 different proteins.

Electrolytes in tears include:

  • sodium, which gives tears their characteristic salty taste
  • bicarbonate
  • chloride
  • potassium

Tears also contain lower levels of magnesium and calcium.

Together, these things make up three distinct layers in your tears:

  • The mucous layer keeps the tear attached to the eye.
  • The aqueous layer — the thickest layer — hydrates your eye, keeps bacteria away, and protects your cornea.
  • The oily layer prevents the other layers from evaporating and also keeps the tear’s surface smooth so that you can see through it.

You have three different types of tears:

  • Basal tears. These are always in your eyes to protect from debris and keep them lubricated and nourished.
  • Reflex tears. These form when your eyes are exposed to irritants, such as smoke and onion fumes.
  • Emotional tears. These are produced when you’re sad, happy, or feeling other intense emotions.

Dry eye syndrome is a common condition that happens when an inadequate quantity or quality of tears fails to lubricate your eyes properly. Dry eye syndrome can cause your eyes to burn, sting, or feel scratchy.

It may seem odd, but dry eyes also often cause watery eyes. The watering is a response to the irritation.

Some causes of dry eye are certain medical conditions, dry air or wind, and staring at a computer screen for prolonged periods.

According to the American Academy of Ophthalmology (AAO), you make 15 to 30 gallons of tears every year.

Your tears are produced by lacrimal glands located above your eyes. Tears spread across the surface of the eye when you blink. They then drain into small holes in the corners of your upper and lower lids before traveling through small channels and down your tear ducts to your nose.

While tear production can slow down due to certain factors, such as health and aging, you don’t actually run out of tears.

You produce fewer basal tears as you get older, which is why dry eyes are more common in older adults. This is especially true for women after menopause due to hormonal changes.

Syn-propanethial-S-oxide is the gas that causes you to tear up when you chop onions. The chemical process that creates the gas is a bit complicated, but also really interesting.

Let’s break it down:

  1. Sulfur in the ground where the onions grow mixes with the onion to create amino sulfides, which turn into a gas that protects growing onions from critters looking for a snack.
  2. The gas mixes with onion enzymes that are released when an onion is chopped, creating sulfenic acid.
  3. Sulfenic acid reacts with the onion enzymes and creates syn-propanethial-S-oxide, which irritates your eyes.
  4. Your eyes produce tears as protection against irritants.

That’s how and why chopping onions makes you cry.

Anything that causes eye irritation can cause your lacrimal glands to produce tears. Some people are more sensitive to irritants than others.

Along with onions, your eyes might also tear up from:

  • strong odors, such as perfumes
  • bright lights
  • vomit
  • dust
  • chemicals, such as chlorine and cleaning products
  • too much screen time
  • reading small print or reading for prolonged periods

Your eyes and nasal passages are connected. When your lacrimal glands produce tears, they drain downward through your tear ducts, which are also called nasolacrimal ducts. This causes your tears to run down through the nasal bone and into the back of your nose and down your throat.

When you cry, producing many tears, the tears mix with the mucus in your nose, which is why your nose runs when you cry.

The purpose of emotional tears is still being researched, but is believed to be influenced by biological, social, and psychological factors.

Some researchers believe that crying is a social signal to get help from others when you’re in pain, sad, or feeling any type of distress or extreme emotion. Often, when you cry, it prompts others to offer support, which makes you feel better.

There is evidence that emotional tears contain additional proteins and hormones that aren’t found in the two other types of tears. These may have relaxing or pain-relieving effects that help regulate the body and help it return to its normal state.

Even if the jury is still out on the purpose of emotional tears, the benefits of crying are well documented.

Crying sends some visual signals. When you see someone cry, it’s a sign that they’re feeling sad or distressed. A 2011 study found that the tears we cry also send signals that others can smell even though tears are actually odorless.

The study used both saline and tears collected from women while they watched a sad movie. The male participants couldn’t smell the difference between the real tears and the saline. But those who sniffed the tears rated female faces less sexually attractive and reported lower sexual excitement, which was confirmed by testing saliva levels and using MRI.

Interestingly, a 2012 study looked at men’s testosterone levels in response to simulated baby tears. Men who had an effective nurturing response to the cries experienced a drop in testosterone. Those who didn’t experienced a rise.

While both of these studies describe effects that aren’t completely understood, the fact remains — tears send messages to others.

The term “crocodile tears” is used to describe someone who is pretending to cry. It came from the myth that crocodiles cry when eating humans, which was coined from the book “The Voyage and Travel of Sir John Mandeville,” published in 1400.

According to a 2007 study, crocodiles may actually cry when they eat. Alligators and caimans — which are closely related to crocodiles — were observed instead of crocodiles. When fed, the animals did shed tears, though the reason for the tears isn’t fully understood.

Newborns don’t produce tears when they cry because their lacrimal glands aren’t fully developed. They may cry without tears for the first month or so of life.

Some babies are born with or develop blocked tear ducts. In these cases, the baby can produce tears but one or both ducts may not be fully open or may be blocked.

Though it happens more often in babies and children, people of all ages can cry in their sleep.

Things that can cause sleep-crying or waking up crying include:

Animals produce tears to lubricate and protect the eye. While they may shed tears in response to irritants and injury, they don’t produce emotional tears like humans do.

There are many claims — a number of them backed by research — that women cry more than men. However, the gap seems to differ depending on part of the world, perhaps due to cultural norms.

No one knows exactly why women may cry more than men. It may have something to do with men having smaller tear ducts and emotional tears containing prolactin, which is a hormone that promotes breast milk production. Women have 60 percent more prolactin than men.

Pseudobulbar affect (PBA) is a condition that can cause uncontrollable tears. It’s characterized by episodes of sudden uncontrollable crying or laughing. The laughing usually turns to tears.

PBA usually affects people with certain neurological conditions or injuries that alter the way the brain controls emotion. Examples of these are stroke, Alzheimer’s disease, Parkinson’s disease, and multiple sclerosis (MS).

Tears keep the surface of your eyes smooth and clear while also protecting against infection. Without enough tears, your eyes are at risk of:

Your tears work hard to protect your eyes, clear out irritants, soothe emotions, and even send messages to those around you.

While there are many reasons why we cry, tears are a sign of health and in some ways — at least in terms of emotional tears — uniquely human.