Ever wonder why water comes out of our eyes when we’re sad or tired or frustrated? Turns out that crying is one of the most unique and perplexing of human behaviors. It is the only physiological function that is unique to humans. And the tears themselves are complex–we actually shed three different kinds. But what is the purpose of turning on the waterworks? It all depends on what caused them.

Basal Tears

These tears are the ones in our eyes all the time that serve to protect, nourish and lubricate the eyes. These tears are chemically different from other types of tears.

Characteristics of basal tears:

  • constantly produced
  • keep dirt and debris away
  • made up of three layers: mucus layer which keeps tears fastened to eye, aqueous layer which keeps in hydration and keeps out invasive bacteria, and an outer lipid layer which keeps the surface smooth

Reflex Tears

The second type of tears know as reflex tears appear in large quantity to protect the eye from irritants such as wind, smoke, or the chemical “syn-propanethial-S-oxide“ in onions.

Characteristics of reflex tears:

Emotional Tears

This type of tears unique to humans is the most mysterious kind of tears. Scientists don’t know exactly why we emotionally cry but there are various theories. One theory according to a study out of Vassar College suggests tears developed as a silent signaling system to let others respond to us when we are vulnerable without alerting predators. Others believe it’s a way to elicit compassion. There’s also the argument that a good cry alleviates stress–85% of women and 73% of men report feeling better afterwards. Lastly, there’s the possibility that tears help build strong communities by eliciting empathy and therefore closer relationships necessary to living in a complex society.

Characteristics of emotional tears:

  • stabailize mood
  • contain high levels of stress hormone ACTH
  • contain encephalin–an endorphin and natural painkiller

Now the next time you’re watching a sad scene in a movie, you will know that your eyes are welling up for a purpose and can reflect on how the tears are an example of the incredibly intricate systems that go into making us humans who we are.

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