Tears raise many questions, the answers to which are very interesting. For example, how does our body receive signals of sadness - or extreme happiness - to trigger tears; and what is even in them? Hopefully, this article will give you an insight into the fascinating science of a tear.  

Firstly, what substances are found in a tear? Well, they mainly consist of water, but also contain salt, fatty oils, and over 1, 500 different types of proteins. A tear has three different layers: the mucous, or continuous, layer, which keeps the tear attached to the eye; the aqueous layer, which is the thickest layer and hydrates your eye, shielding it from bacteria, as well as protecting your cornea (the transparent layer that covers the front of your eyeball); and finally the oily layer, which prevents the other layers from evaporating. 

However, you actually have three different types of tears. Basal tears are permanently in your eyes and keep them lubricated. Emotional tears are the kind that we are most familiar with, which are produced when we experience intense and severe emotions. The final one is the reflex tear, which is emitted when our eyes are exposed to irritants, like onions or smoke. 

Where do tears go after they have been created? 

There are lacrimal glands (glands that constantly release moisture to hydrate your eyes) stationed above your eyes. As you blink, tears spread on the surface of your eye and then drain into tiny holes in the corners of your lower and upper lids. Then, they travel through small channels and down your tear ducts to your nose.  

How do our bodies receive signals to generate tears?  

When it comes to emotional tears, first, the amygdala, the area of brain that controls the processing of emotions, sends signals to the hypothalamus, a small, spherical gland in the brain that is connected to the autonomic nervous system. The autonomic nervous system handles functions that we cannot control, like body temperature, hunger, thirst and crying. The hypothalamus then starts the sympathetic nervous system (the system that prompts localised adjustments like sweating), and accelerates the response to this. This results in your glottis (the opening between the vocal cords in your throat) to swell, making your throat feel tight. All your emotions tell the hypothalamus to produce a specific compound, acetylcholine. Acetylcholine links to receptors in your brain which send signals to your lacrimal glands, which then produce tears.  

When your eyes are exposed to irritants such as onions and strong odours like perfume, we often experience a few tears; but why? Syn-Propanethial-S-oxide is the gas that causes you to cry when chopping onions. The process? When onions are growing, they mix with the sulphur in the ground and create amino sulphides which turn into a gas. Then this gas combines itself with the enzymes released from the onion when you chop it, creating sulfenic acid, which reacts with the onion enzymes to form syn-Propanethial-S-oxide; finally, your lacrimal glands attempt to protect your eyes and produce reflex tears. Other examples of eye irritants are smoke, bright lights and reading small print for an extended period of time.  

Why do we get a runny nose when we cry?  

When your emotional tears run through your tear ducts, also known as nasolachrymal ducts, they end up in your nasal passage. They then mix with the mucus in your nose, causing your nose to run.  

Does your age and sex affect your body’s production and tolerance for tears?  

It is true that the older you are, the less basal tears that you produce. Your gender can similarly regulate your tolerance for tears. The assumption that women cry more than men is often viewed as sexist, and there are a few studies to prove this stereotype as actually true. This has not been thoroughly investigated and so is not a confirmed statement, but scientists believe that, if it is true, it is down to two theories: that men may have smaller tear ducts than women, or that it is because of the higher quantity of prolactin in women’s emotional tears. Prolactin is a hormone that helps breast milk production in females. Women have 60% more prolactin than men.  

What is dry eye syndrome?  

Dry eye syndrome is a widespread condition in which you lack basal tears. As the name suggests, it means that your eyes are too dry and this may cause them to sting, burn, or feel scratchy. Strangely, these feelings might cause your eyes to water as a response to the irritation. Dry eye syndrome can be caused by age, lengthened screen time, or dry air or wind. 

Are there any health benefits to crying?  

Emotional tears contain stress hormones and other toxins. Scientists speculate that these are flushed away when we cry. A good cry also makes us feel indisputably better. 

Do babies actually release tears when they cry? 

Because babies’ lacrimal glands aren’t fully developed, babies are unable to produce any tears. However, this only lasts for the first month or so of your life.  

In conclusion, tears encompass an immense quantity of curiosity and research, covering many riveting subjects. Though we already know so much, there is always room for further investigation. How long can we cry for before we just cannot produce anymore tears?

Is Haemolacria (when you produce blood-tinged tears) a symptom of other medical conditions? Are tears a form of excretion? Like all other pieces of scientific data, they only show what we know, without addressing what we do not. There are still so many questions yet to be answered, and maybe you could be the one to find them out. I hope that you now have a better understanding of this intriguing field and the fascinating science of a tear.