
Tears are a clear liquid secreted by the
lacrimal gland
The lacrimal glands are paired exocrine glands, one for each eye, found in most terrestrial vertebrates and some marine mammals, that secrete the aqueous layer of the tear film. In humans, they are situated in the upper lateral region of each o ...
s (tear gland) found in the
eyes of all
land mammals. Tears are made up of water, electrolytes, proteins, lipids, and mucins that form layers on the surface of eyes.
The different types of tears—basal, reflex, and emotional—vary significantly in composition.

The functions of tears include lubricating the eyes (basal tears), removing irritants (reflex tears), and also aiding the
immune system
The immune system is a network of biological systems that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to bacteria, as well as Tumor immunology, cancer cells, Parasitic worm, parasitic ...
.
Tears also occur as a part of the body's natural pain response.
Emotional secretion of tears may serve a biological function by excreting stress-inducing hormones built up through times of emotional distress. Tears have
symbolic significance among humans.
Physiology
Chemical composition
Tears are made up of three layers: lipid, aqueous, and mucous.
Tears are composed of
water
Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...
,
salt
In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...
s,
antibodies
An antibody (Ab) or immunoglobulin (Ig) is a large, Y-shaped protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as bacteria and viruses, including those that caus ...
, and
lysozyme
Lysozyme (, muramidase, ''N''-acetylmuramide glycanhydrolase; systematic name peptidoglycan ''N''-acetylmuramoylhydrolase) is an antimicrobial enzyme produced by animals that forms part of the innate immune system. It is a glycoside hydrolase ...
s (antibacterial enzymes); though composition varies among different tear types. The composition of tears caused by an emotional reaction differs from that of tears as a reaction to irritants, such as onion fumes, dust, or allergens. Emotional tears contain higher concentrations of stress hormones such as
adrenocorticotropic hormone and
leucine enkephalin (a natural pain killer), which suggests that emotional tears play a biological role in balancing stress hormone levels.
Drainage of tear film
The
lacrimal gland
The lacrimal glands are paired exocrine glands, one for each eye, found in most terrestrial vertebrates and some marine mammals, that secrete the aqueous layer of the tear film. In humans, they are situated in the upper lateral region of each o ...
s secrete lacrimal fluid, which flows through the main excretory ducts into the space between the eyeball and the lids.
When the eyes blink, the lacrimal fluid is spread across the surface of the eye.
Lacrimal fluid gathers in the
lacrimal lake
The lacrimal lake is the pool of tears in the lower conjunctival cul-de-sac, which drains into the opening of the tear drainage system (the '' puncta lacrimalia''). The volume of the lacrimal lake has been estimated to be between 7 and 10 ...
which is found in the medial part of the eye. The lacrimal papilla is an elevation in the inner side of the eyelid, at the edge of the lacrimal lake.
The lacrimal canaliculi open into the papilla.
The opening of each canaliculus is the lacrimal punctum. From the punctum, tears will enter the
lacrimal sac
The lacrimal sac or lachrymal sac is the upper dilated end of the nasolacrimal duct, and is lodged in a deep groove formed by the lacrimal bone and frontal process of the maxilla. It connects the lacrimal canaliculi, which drain tears from th ...
,
then on to the
nasolacrimal duct
The nasolacrimal duct (also called the tear duct) carries tears from the lacrimal sac of the eye into the nasal cavity. The duct begins in the eye socket between the maxillary and lacrimal bones, from where it passes downwards and backwards. ...
, and finally into the
nasal cavity
The nasal cavity is a large, air-filled space above and behind the nose in the middle of the face. The nasal septum divides the cavity into two cavities, also known as fossae. Each cavity is the continuation of one of the two nostrils. The nas ...
.
An excess of tears, as caused by strong
emotion
Emotions are physical and mental states brought on by neurophysiology, neurophysiological changes, variously associated with thoughts, feelings, behavior, behavioral responses, and a degree of pleasure or suffering, displeasure. There is ...
, can cause the nose to run. Quality of vision is affected by the stability of the tear film.
Types
There are three basic types of tears: basal, reflex and emotional.
Nictitating membrane
Some mammals, such as
cats,
camel
A camel (from and () from Ancient Semitic: ''gāmāl'') is an even-toed ungulate in the genus ''Camelus'' that bears distinctive fatty deposits known as "humps" on its back. Camels have long been domesticated and, as livestock, they provid ...
s,
polar bear
The polar bear (''Ursus maritimus'') is a large bear native to the Arctic and nearby areas. It is closely related to the brown bear, and the two species can Hybrid (biology), interbreed. The polar bear is the largest extant species of bear ...
s,
seals and
aardvarks, have a full translucent third eyelid called a
nictitating membrane, while others have a
vestigial nictitating membrane. The membrane works to protect and moisten the eyelid while maintaining visibility. It also contributes to the aqueous portion of the tear film and possibly immunoglobulins. Humans and some primates have a much smaller nictitating membrane; this may be because they do not capture prey or root vegetation with their teeth, so that there is no evolutionary advantage of the third eyelid.
Neurology
The
trigeminal V
1 (fifth cranial) nerve bears the sensory pathway of the tear reflexes. When the trigeminal nerve is cut, tears from reflexes will stop, while emotional tears will not. The great (superficial) petrosal nerve from cranial nerve VII provides autonomic innervation to the lacrimal gland. It is responsible for the production of much of the aqueous portion of the tear film.
Human culture

In nearly all human cultures,
crying is associated with tears, active tear ducts and abrupt strong respiration, due to strong emotional impetuses. Triggers of crying can vary from sadness and
grief
Grief is the response to the loss of something deemed important, particularly to the death of a person to whom or animal to which a Human bonding, bond or affection was formed. Although conventionally focused on the emotional response to loss, ...
to intense anger, happiness, fear, mirth,
frustration
In psychology, frustration is a common emotional response to opposition, related to anger, annoyance and disappointment. Frustration arises from the perceived resistance to the fulfillment of an individual's Will (philosophy), will or goal and ...
, confusion, and any form of overwhelming stimuli. Emotional tears can also be triggered by social and personal experiences, like listening to music, reading social media content, sharing thoughts, and communicating.
Crying is often associated with babies and children. The infants that are unable to vocally communicate have many alternating tones in their crying, attracting the attention of the caregiver and specifically their biological mothers.
Blood-related mothers goes through physiological changes upon exposure to the crying, with acceleration in muscles and decrease in heart rate, as well as understanding the vocalizations of the baby's crying.
This is a mother-specific case, as the other caregivers, like biological father or adoptive parents, are not able to decode the sound.
Some cultures consider crying to be undignified and infantile, casting aspersions on those who cry in public settings, excluding circumstances which concerns loss of a relative or a loved one. In most Western cultures, it is more socially acceptable for women and children to cry than men, reflecting masculine sex-role stereotypes.
In some Latin regions, crying among men is more acceptable. There is evidence for an interpersonal function of crying as tears express a need for help and foster willingness to help in an observer.
Some modern
psychotherapy
Psychotherapy (also psychological therapy, talk therapy, or talking therapy) is the use of Psychology, psychological methods, particularly when based on regular Conversation, personal interaction, to help a person change behavior, increase hap ...
movements such as
Re-evaluation Counseling encourage crying as beneficial to health and mental well-being. An insincere display of grief or dishonest remorse is sometimes called
crocodile tears in reference to an Ancient Greek anecdote that crocodiles would pretend to weep while luring or devouring their prey. In addition, "crocodile tears syndrome" is a colloquialism for
Bogorad's syndrome, an uncommon consequence of recovery from
Bell's palsy in which faulty regeneration of the facial nerve causes people to shed tears while eating.
Pathology
Bogorad's syndrome
Bogorad's syndrome, also known as "Crocodile Tears Syndrome", is an uncommon consequence of nerve regeneration subsequent to
Bell's palsy or other damage to the
facial nerve
The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of ta ...
. Efferent fibers from the
superior salivary nucleus become improperly connected to nerve axons projecting to the
lacrimal glands, causing one to shed tears (
lacrimate) on the side of the palsy during salivation while smelling foods or eating. It is presumed that this would cause salivation while crying due to the inverse improper connection of the lacrimal nucleus to the salivary glands, but this would be less noticeable.
The condition was first described in 1926 by its namesake, Russian neuropathologist F. A. Bogorad, in an article titled "Syndrome of the Crocodile Tears" (alternatively, "The Symptom of the Crocodile Tears") that argued the tears were caused by the act of salivation.
Keratoconjunctivitis sicca (dry eye)
Keratoconjunctivitis sicca, known in the vernacular as dry eye, is a very common disorder of the tear film. Despite the eyes being dry, those affected can still experience watering of the eyes, which is, in fact, a response to irritation caused by the original tear film deficiency. Lack of Meibomian gland secretion can mean that the tears are not enveloped in a hydrophobic film coat, leading to tears spilling onto the face.
Treatment for dry eyes to compensate for the loss of tear film include eye-drops composed of methyl cellulose or carboxy- methyl cellulose or hemi-cellulose in strengths of either 0.5% or 1% depending upon the severity of drying up of the cornea.
Familial dysautonomia
Familial dysautonomia is a genetic condition that can be associated with a lack of overflow tears (
Alacrima) during emotional crying.
Obstruction of the
punctum,
nasolacrimal canal, or
nasolacrimal duct
The nasolacrimal duct (also called the tear duct) carries tears from the lacrimal sac of the eye into the nasal cavity. The duct begins in the eye socket between the maxillary and lacrimal bones, from where it passes downwards and backwards. ...
can cause even normal levels of the basal tear to overflow onto the face (
Epiphora), giving the appearance of constant psychic tearing. This can have significant social consequences.
Pseudobulbar affect
Pseudobulbar affect
Pseudobulbar affect (PBA), or emotional incontinence, is a type of affect disorder connected to Neurological condition, neurological conditions. It is characterized by brief, intense, uncontrollable episodes of crying or laughter, laughing. The ...
(PBA) is a condition involving episodic uncontrollable laughter or crying. PBA mostly occurs in people with neurological injuries affecting how the brain controls emotions. Scientists believe PBA results from prefrontal cortex damage. PBA often involves crying. Hence, PBA is mistakable for depression. But PBA is neurological; depression is psychological.
Patients with PBA do not experience typical depression symptoms like sleep disturbances or appetite loss.
See also
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Artificial tears
*
Dacryocystocele
*
Epiphora
*
Eye
*
Eyelid
*
Professional mourning
*
Sadness
Sadness is an emotional pain associated with, or characterized by, feelings of disadvantage, loss, despair, grief, helplessness, disappointment and sorrow. An individual experiencing sadness may become quiet or lethargic, and withdraw the ...
*
Harderian gland
References
External links
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{{Authority control
Crying
Human physiology
Eye
Body fluids