Will any one believe that on an average men cry once in every month while women shed tears 5 times a month? What about a chef who cuts onion every day as a part of his daily routine? Probably it must be a 24X7 situation, all around the year. According to scientists and psychologists, there are three types of tears which include 'basal' tears, 'reflex' tears and 'emotional' or 'psychic' tears. Basal tears are more or less continuous to keep cornea wet and nourished, besides cleaning it free of dust. It contains water, mucin, lipids, lysozome, lactoferrin, lipocatin, lacretrin, immunoglobulins, glucose, urea, sodium and potassium. Some of these substances are responsible for fighting bacterial infection that may affect the eyes. In a 24 hour period humans secrete about 0.75 to 1.1 gm of tears.
Reflex crying is not in response to any normal state and is caused by some irritation due to foreign particles or presence of irritant substances like vapors generated during cutting of onion, or tear gas or pepper spray near the eyes. Bright light can also make eyes shed tears. Hot or peppery stimulii to the tongue and mouth can cause secretion of tears. Capsaicin in chilli, piperine in black pepper and gingerols and shogaols in ginger create such stimulii when taken in high concentrations. When onion is cut the volatile sulfur chemicals generated by enzyme action, react with the water in the tears to form acidic compounds which irritate the eyes causing tears to flow through the cheeks. There is an amusing report that 'tearless' onion varieties have been developed by suppressing the RNAi gene responsible for generating volatile tear-causing chemicals when it is cut but whether it is acceptable to the consumer remains to be seen.
Emotional tears result from strong emotional stress, suffering and physical pain and such crying is some times accompanied by reddening of the face, sobbing, coughing and convulsive breathing. Emotional tears have different composition, being richer in prolactin, adrenocorticotropic hormone and leucine enkaphalin. A neuronal connection between the tear duct and brain is known to exist and emotional tears are produced on a signal from the brain in response to emotional stresses. One always feels better after crying because of elimination of stress hormones. Increased mucal excretion occurs during crying giving a feeling of being light afterwards. In many cases an underlying experience of helplessness is manifested in crying. Good news invariably evokes crying because of helplessness in influencing what is happening.
Crying ability can be compromised by some disorders like Bell's Palsy due to faulty facial nerves or Familial Dysautonomia due to lack of overflowing tears or pathological laughing and crying disorder. 'Crocodile tear syndrome' is manifested by shedding tears during eating due to problems with the facial nerve. The expression 'Crocodile tears' in colloquial use refers to insincere display of grief or dishonest remorse by people. Do animals cry? Some believe that elephants, gorillas and camels do cry due to emotions but one is never sure. Lachrymators are volatile chemical substances that provoke tears and include compounds containing CS, CR, bromoacetone, phenacyl bromide, xylyl bromide etc. The famous 'tear gas', used world wide for crowd control by law enforcement agencies is 2-chlorobenzalmalononitrile which stimulates the corneal nerves in the eyes to cause profuse tears and a burning sensation, without causing any permanent damage.
One of the most studied "crying phenomena" is that encountered in babies. There are many reasons for a baby to cry which include acid reflux, food allergies like cow's milk, overactive let down (OALD) caused by too much milk flow causing even choking, teething trouble, pyloric stenosis, colic problem etc and pediatricians usually have difficulties in finding out the exact cause in many cases. One wonders whether there is any truth in the old saying that "crying baby only will get the milk"! What about the common saying, 'crying over split-milk',to stop thinking about the past? Then we have the expression, crocodile tears which has nothing to do with the ferocious amphibian creature. Probably one can only cry when faced with a complex phenomenon as crying!