MORE THAN A SIGN OF SADNESS

We cry when we're sad. We cry when we're happy. We cry when we chop onions. We cry when we are in pain. We cry when we have an eyelash in our eye. Tears serve a number of different functions, but the fundamental one is to keep the eyes healthy by lubricating them and flushing out debris. As well as the various different reasons for crying, our tears are made up of various different substances. Tears contain water for moisture, oils for lubrication and mucus for resistance to infection and even spreading across the surface of the eyes. Because there are no blood vessels on the surface of the eyes, tears transport oxygen and nutrients to the surface cells.

The Origin of Tears

For centuries, people thought tears originated in the heart. Later, in Hippocrates' time, it was thought that the mind was the trigger for tears. Finally, in 1662, a Danish scientist named Niels Stensen discovered that the lacrimal gland was the origin point of tears. His theory was that tears were simply a way to keep the eyes moist.

Types of Tears

There are three kinds of tears, each of which has a different function.

Basal tears, which contain oil, mucus, water and salt keep the eyes hydrated and help fight infection. They flow continuously from the lacrimal glands, moistening the eyes each time we blink.

Reflex tears form when the eyes are exposed to irritants, such as smoke and onion fumes, flushing out the material causing the irritation. They contain antibodies to prevent micro-organisms from harming the eyes. They may even be triggered by eye strain or fatigue due to excessive screen time or reading in dim light.

Psychic or emotional tears appear in response to emotion and have a different chemical composition from other tears. They have a similar makeup to basal tears but contain more substances which help to remove chemicals that build up during stress, as well as an endorphin which reduces pain and improves mood, literally making us feel better after a "good cry".

Enough Tears

Crying is a uniquely human behaviour caused by a variety of factors, but it's possible to ‘cry' too much or not ‘cry' enough. The eyes can temporarily dry out because of atmospheric conditions, and there are a number of health conditions and medications that cause the eyes to produce insufficient tears or tears of poor quality.

With dry eye syndrome an inadequate quantity or quality of tears causes the eyes to burn, feel scratchy and water excessively as a response to the irritation. When we have a cold, the tear ducts may become swollen or blocked, resulting in tears overflowing instead of draining into the nose.

Tears Flow Continuously

Tears are produced by the lacrimal glands which produce 15 to 30 gallons of tears every year. While tear production can slow down due to certain factors, such as health conditions, hormonal changes and aging, we don't run out of tears. As we age, we produce fewer basal tears which is why dry eyes are more common in older people.

Tears and Gender

Research has shown that in childhood boys and girls do equal amounts of crying. Once they enter adolescence, boys cry less than girls as their level of testosterone increases, while frequency of crying in girls increases with their oestrogen levels. Although there may be cultural differences, generally females have been found to cry up to four times as much as males do.

Babies' Tears

While crying in babies obviously serves the crucial function of demanding attention and care, newborn babies don't produce tears when they cry because their lacrimal glands aren't fully developed. They may cry without tears for the first few weeks of life.

Laugh Until you Cry

One explanation for laughing so hard that tears are shed is that both laughing and crying happen during times of high emotional arousal, and that the same part of the brain is responsible for both crying and laughing. Another explanation suggests that pressure is put on the tear ducts as a result of a vigorous laugh. These tears are considered reflex tears rather than being due to emotion.

Yawning and Tears

It is common for the eyes to water when we yawn. Yawning usually includes opening the mouth wide and scrunching the muscles around the eyes which puts pressure on the lacrimal glands, increasing the secretion of tears.

Animals' Tears

Animals produce tears, but emotions have nothing to do with it; the emotional component of tears is uniquely human. Animals may make crying sounds, but tears are not shed in response to emotional or physical stress. Animals' tears lubricate and protect the eyes and may be shed in response to irritants and injury.

Crocodile Tears

The term "crocodile tears" means an insincere expression of emotion and is used to describe someone who is pretending to cry. It originates from a myth that crocodiles cry while devouring their prey.

Research into tears and their function, both physiologically and psychologically, is ongoing as scientists unravel the mysteries of why we cry and how different reasons for crying affect the chemical composition of our tears.