Nipple
Encyclopedia
In its most general form, a nipple is a structure
from which a fluid emanates. More specifically, it is the projection on the breast
s or udder
of a mammal by which breast milk
is delivered to a mother's young. In this sense, it is often called a teat, especially when referring to non-humans, and the medical term used to refer to it is papilla. The rubber mouthpiece of a baby bottle
or pacifier
may also be referred to as a "nipple" or a "teat".
of neb, an Old English word meaning "beak", "nose", or "face", and which is of Germanic origin. The words teat and tit share a Germanic ancestor. The second of the two, tit, was inherited directly from Proto-Germanic, while the first entered English via Old French
.
of mammal
s, a nipple or mammary papilla or teat is a small projection of skin
containing the outlets for 15-20 lactiferous duct
s arranged cylindrically around the tip. The skin of the nipple is rich in a supply of special nerve
s that are sensitive to certain stimuli. The physiological purpose of nipples is to deliver milk
to the infant, produced in the female mammary gland
s during lactation
.
Marsupial
s and eutherian mammals
typically have an even number of nipples arranged bilaterally, from as few as two to as many as 20. They develop in the embryo
, along the 'milk line
s'. Most mammals develop multiple nipples along each milk line, with the total number approximating the maximum litter size, and half the total number (i.e. the number on one side) approximating the average litter size for that species. Monotremes, such as the platypus
, lack teats; their young drink milk directly from pores in the skin (similar to sweat
glands), or by sucking it off of hairs surrounding the pores.
In cetaceans such as whales, the infant cannot form a suction-seal to nurse, due to its mouth structure; the whale's nipple is therefore unlike that of any other mammal. Rather than requiring a sucking action, the discharge of milk is powered by maternal muscles. The calf takes the extended nipple into its mouth, and the mother ejects or expels her milk into the mouth of the calf.
Teats vary in size, location, and structure in different mammalian species. Teats, on occasion, become so plump and filled that milk may escape without suckling. Female goats and ewes have two teats, each with a single mammary gland, located between the hindlegs. Mares have two teats, each with two mammary glands. The teats of the sow
can be quite variable in number, from six to thirty, and are located on two parallel lines along the belly. Cows have four teats, each with one mammary gland in the udder. Humans have two teats. Extra teats occur often, and are known as supernumerary teats
. They are nonfunctional.
In most eutherian mammals, both males and females have teats. In the male
, nipples are often not considered functional with regard to breastfeeding
, although male lactation
is possible. Notable exceptions to this are rat
s and horse
s, neither of which has teats in the male.
The pigments of the nipple and areola
are brown eumelanin, a brown pigment, and to a greater extent pheomelanin, a red pigment. In many women, there are small bulges on the areola, which are called 'Montgomery bodies'. In humans, the nipple is innervated by the fourth intercostal nerve.
occurs in most species within minutes of birth, and serves both to connect the young to the food source and to encourage bonding
between mother and young. The offspring thoroughly enjoy their suckling time, and may suckle even after filling up.
s have two nipples after birth, located near the centre of each breast
and surrounded by an area of sensitive, pigmented skin known as the areola. Human fetuses develop several more nipples along the milk lines, which extend from the axilla (armpit), along the abdominal muscles, and down to the pubis
(groin) on both sides. Those nipples usually disappear before birth, but sometimes remain, resulting in supernumerary nipple
s which uncommonly have lactiferous glands attached. Sometimes, babies, male or female, are born producing milk. This is common and is colloquially called 'witch's milk'. It is caused by maternal estrogen
s acting on the baby and disappears after several days.
, but due to the contraction of smooth muscle
under the control of the autonomic nervous system
. It is more akin to a hair follicle
standing on end than to a sexual erection. Nipple erections are a product of the pilomotor reflex which causes goose bumps
. The erection of the nipple is partially due to the cylindrically-arranged muscle cells found within it.
Nipple erection can also be caused by a tactile response to cold temperature in both males and females. Nipple erection may also result during sexual arousal
in females and males, or during breastfeeding
. Both are caused by the release of oxytocin
.
s, which are generally stimulated by hands or by mouth during foreplay
, which leads to sexual arousal
. While female nipples and areolae have been shown to have greater levels of innervation, female nipples are also more sensitive, likely due to hormonal influences as well. During arousal they generally become stiff, erect and protrude out.
The nipple and areola
of males and females can be erotic receptors, sometimes intense enough to elicit orgasm
in some individuals of either sex.
, all mammalian fetus
es within the same species
look the same, regardless of sex. In humans, this lasts for around 6 weeks; after which genetically-male fetuses begin producing male hormone
s such as testosterone
. Usually, males' nipples do not change much past this point; however, some males develop a condition known as gynecomastia
, in which the fatty tissue around and under the nipple develops into something similar to a female breast. This may happen whenever the testosterone level drops. Gynecomastia, although not as severe, may occur in pubescent boys undergoing physical changes due to the rapid and uncontrolled release of hormones, including estrogen. The heightened levels of oestrogen in pubescent male bodies leads to the swelling of the nipple and surrounding tissue - this can often look similar to a female human nipple - and may cause slight discomfort.
Thus, because the "female template" is the default for humans, the question is not why evolution
has not selected against male nipples, but why it would be advantageous to select against male nipples in the first place:
Structure
Structure is a fundamental, tangible or intangible notion referring to the recognition, observation, nature, and permanence of patterns and relationships of entities. This notion may itself be an object, such as a built structure, or an attribute, such as the structure of society...
from which a fluid emanates. More specifically, it is the projection on the breast
Breast
The breast is the upper ventral region of the torso of a primate, in left and right sides, which in a female contains the mammary gland that secretes milk used to feed infants.Both men and women develop breasts from the same embryological tissues...
s or udder
Udder
An udder is an organ formed of the mammary glands of female quadruped mammals, especially ruminants such as cattle, goats, sheep and deer. The udder is a single mass hanging beneath the animal, consisting of pairs of mammary glands...
of a mammal by which breast milk
Breast milk
Breast milk, more specifically human milk, is the milk produced by the breasts of a human female for her infant offspring...
is delivered to a mother's young. In this sense, it is often called a teat, especially when referring to non-humans, and the medical term used to refer to it is papilla. The rubber mouthpiece of a baby bottle
Baby bottle
A baby bottle is a bottle with a teat to drink directly from. It is typically used by infants and young children when a mother does not breastfeed, or if someone cannot drink from a cup, for feeding oneself or being fed.In particular it is used to feed infant formula, expressed breast milk or...
or pacifier
Pacifier
A pacifier is a rubber, plastic, or silicone nipple given to an infant or other young child to suck upon. In its standard appearance it has a teat, mouth shield, and handle...
may also be referred to as a "nipple" or a "teat".
Etymology
The word nipple most likely originates as a diminutiveDiminutive
In language structure, a diminutive, or diminutive form , is a formation of a word used to convey a slight degree of the root meaning, smallness of the object or quality named, encapsulation, intimacy, or endearment...
of neb, an Old English word meaning "beak", "nose", or "face", and which is of Germanic origin. The words teat and tit share a Germanic ancestor. The second of the two, tit, was inherited directly from Proto-Germanic, while the first entered English via Old French
Old French
Old French was the Romance dialect continuum spoken in territories that span roughly the northern half of modern France and parts of modern Belgium and Switzerland from the 9th century to the 14th century...
.
Anatomy
In the anatomyAnatomy
Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...
of mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s, a nipple or mammary papilla or teat is a small projection of skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
containing the outlets for 15-20 lactiferous duct
Lactiferous duct
Lactiferous ducts lead from the lobules of the mammary gland to the tip of the nipple. They are also referred to as galactophores, galactophorous ducts, mammary ducts, mamillary ducts and milk ducts...
s arranged cylindrically around the tip. The skin of the nipple is rich in a supply of special nerve
Nerve
A peripheral nerve, or simply nerve, is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...
s that are sensitive to certain stimuli. The physiological purpose of nipples is to deliver milk
Milk
Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...
to the infant, produced in the female mammary gland
Mammary gland
A mammary gland is an organ in mammals that produces milk to feed young offspring. Mammals get their name from the word "mammary". In ruminants such as cows, goats, and deer, the mammary glands are contained in their udders...
s during lactation
Lactation
Lactation describes the secretion of milk from the mammary glands and the period of time that a mother lactates to feed her young. The process occurs in all female mammals, however it predates mammals. In humans the process of feeding milk is called breastfeeding or nursing...
.
Marsupial
Marsupial
Marsupials are an infraclass of mammals, characterized by giving birth to relatively undeveloped young. Close to 70% of the 334 extant species occur in Australia, New Guinea, and nearby islands, with the remaining 100 found in the Americas, primarily in South America, but with thirteen in Central...
s and eutherian mammals
Eutheria
Eutheria is a group of mammals consisting of placental mammals plus all extinct mammals that are more closely related to living placentals than to living marsupials . They are distinguished from noneutherians by various features of the feet, ankles, jaws and teeth...
typically have an even number of nipples arranged bilaterally, from as few as two to as many as 20. They develop in the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
, along the 'milk line
Milk line
The milk lines are two parallel lines, formed by thickenings of the epidermis along the ventral surface of mammals of both sexes. They extend from the upper limbs to the lower limbs and are developed in the embryo...
s'. Most mammals develop multiple nipples along each milk line, with the total number approximating the maximum litter size, and half the total number (i.e. the number on one side) approximating the average litter size for that species. Monotremes, such as the platypus
Platypus
The platypus is a semi-aquatic mammal endemic to eastern Australia, including Tasmania. Together with the four species of echidna, it is one of the five extant species of monotremes, the only mammals that lay eggs instead of giving birth to live young...
, lack teats; their young drink milk directly from pores in the skin (similar to sweat
SWEAT
SWEAT is an OLN/TSN show hosted by Julie Zwillich that aired in 2003-2004.Each of the 13 half-hour episodes of SWEAT features a different outdoor sport: kayaking, mountain biking, ice hockey, beach volleyball, soccer, windsurfing, rowing, Ultimate, triathlon, wakeboarding, snowboarding, telemark...
glands), or by sucking it off of hairs surrounding the pores.
In cetaceans such as whales, the infant cannot form a suction-seal to nurse, due to its mouth structure; the whale's nipple is therefore unlike that of any other mammal. Rather than requiring a sucking action, the discharge of milk is powered by maternal muscles. The calf takes the extended nipple into its mouth, and the mother ejects or expels her milk into the mouth of the calf.
Teats vary in size, location, and structure in different mammalian species. Teats, on occasion, become so plump and filled that milk may escape without suckling. Female goats and ewes have two teats, each with a single mammary gland, located between the hindlegs. Mares have two teats, each with two mammary glands. The teats of the sow
Pig
A pig is any of the animals in the genus Sus, within the Suidae family of even-toed ungulates. Pigs include the domestic pig, its ancestor the wild boar, and several other wild relatives...
can be quite variable in number, from six to thirty, and are located on two parallel lines along the belly. Cows have four teats, each with one mammary gland in the udder. Humans have two teats. Extra teats occur often, and are known as supernumerary teats
Supernumerary nipple
A supernumerary nipple is an additional nipple occurring in mammals, including humans...
. They are nonfunctional.
In most eutherian mammals, both males and females have teats. In the male
Male
Male refers to the biological sex of an organism, or part of an organism, which produces small mobile gametes, called spermatozoa. Each spermatozoon can fuse with a larger female gamete or ovum, in the process of fertilization...
, nipples are often not considered functional with regard to breastfeeding
Breastfeeding
Breastfeeding is the feeding of an infant or young child with breast milk directly from female human breasts rather than from a baby bottle or other container. Babies have a sucking reflex that enables them to suck and swallow milk. It is recommended that mothers breastfeed for six months or...
, although male lactation
Male lactation
Male lactation in zoology means production of milk from mammary glands in the presence of physiological stimuli connected with nursing infants. It is well documented in the Dayak fruit bat.The term male lactation is not used in human medicine...
is possible. Notable exceptions to this are rat
Rat
Rats are various medium-sized, long-tailed rodents of the superfamily Muroidea. "True rats" are members of the genus Rattus, the most important of which to humans are the black rat, Rattus rattus, and the brown rat, Rattus norvegicus...
s and horse
Horse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
s, neither of which has teats in the male.
The pigments of the nipple and areola
Areola
This article is about the breast tissue. For the entomology term, see the glossary of Lepidopteran terms. For an artistic cloud motif, see aureola. For the cactus feature, see Areole....
are brown eumelanin, a brown pigment, and to a greater extent pheomelanin, a red pigment. In many women, there are small bulges on the areola, which are called 'Montgomery bodies'. In humans, the nipple is innervated by the fourth intercostal nerve.
Instinct
Mammalian infants have a rooting instinct (moving their head so as to bring their mouth towards whatever is touching their face) for seeking the nipple, and a suckling instinct for extracting milk. The offspring of domestic animals, including piglets, calves, lambs, and foals, engage in a behavior known as teat seeking, sipping, and suckling. This strong instinctInstinct
Instinct or innate behavior is the inherent inclination of a living organism toward a particular behavior.The simplest example of an instinctive behavior is a fixed action pattern, in which a very short to medium length sequence of actions, without variation, are carried out in response to a...
occurs in most species within minutes of birth, and serves both to connect the young to the food source and to encourage bonding
Maternal bond
The maternal bond is typically the relationship between a mother and her child.While it typically occurs due to pregnancy and childbirth, it may also occur between a woman and an unrelated child, such as in adoption...
between mother and young. The offspring thoroughly enjoy their suckling time, and may suckle even after filling up.
In infants
Most humanHuman
Humans are the only living species in the Homo genus...
s have two nipples after birth, located near the centre of each breast
Breast
The breast is the upper ventral region of the torso of a primate, in left and right sides, which in a female contains the mammary gland that secretes milk used to feed infants.Both men and women develop breasts from the same embryological tissues...
and surrounded by an area of sensitive, pigmented skin known as the areola. Human fetuses develop several more nipples along the milk lines, which extend from the axilla (armpit), along the abdominal muscles, and down to the pubis
Pubis
Pubis may refer to:* Pubis * Mons pubis, a padding of fat that protects the pubis bone...
(groin) on both sides. Those nipples usually disappear before birth, but sometimes remain, resulting in supernumerary nipple
Supernumerary nipple
A supernumerary nipple is an additional nipple occurring in mammals, including humans...
s which uncommonly have lactiferous glands attached. Sometimes, babies, male or female, are born producing milk. This is common and is colloquially called 'witch's milk'. It is caused by maternal estrogen
Estrogen
Estrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal...
s acting on the baby and disappears after several days.
Erection
The erection of nipples is not due to erectile tissueErectile tissue
Erectile tissue is tissue in the body that can become erect, usually by becoming engorged with blood.-Erectile tissue in the clitoris and penis:...
, but due to the contraction of smooth muscle
Smooth muscle
Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...
under the control of the autonomic nervous system
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
. It is more akin to a hair follicle
Hair follicle
A hair follicle is a skin organ that produces hair. Hair production occurs in phases, including a growth phase , and cessation phase , and a rest phase . Stem cells are principally responsible for the production of hair....
standing on end than to a sexual erection. Nipple erections are a product of the pilomotor reflex which causes goose bumps
Goose bumps
Goose bumps, also called goose flesh, goose pimples, chill bumps, chicken skin, funky spots, Dasler Bumps, chicken bumps or the medical term cutis anserina, are the bumps on a person's skin at the base of body hairs which may involuntarily develop when a person is cold or experiences strong...
. The erection of the nipple is partially due to the cylindrically-arranged muscle cells found within it.
Nipple erection can also be caused by a tactile response to cold temperature in both males and females. Nipple erection may also result during sexual arousal
Sexual arousal
Sexual arousal, or sexual excitement, is the arousal of sexual desire, during or in anticipation of sexual activity. Things that precipitate human sexual arousal are called erotic stimuli, or colloquially known as turn-ons. There are many potential stimuli, both physical or mental, which can cause...
in females and males, or during breastfeeding
Breastfeeding
Breastfeeding is the feeding of an infant or young child with breast milk directly from female human breasts rather than from a baby bottle or other container. Babies have a sucking reflex that enables them to suck and swallow milk. It is recommended that mothers breastfeed for six months or...
. Both are caused by the release of oxytocin
Oxytocin
Oxytocin is a mammalian hormone that acts primarily as a neuromodulator in the brain.Oxytocin is best known for its roles in sexual reproduction, in particular during and after childbirth...
.
Changes in size
The average projection and size of human female nipples is slightly more than 3/8 of an inch (10mm). Pregnancy and nursing tend to increase nipple size, sometimes permanently. Pregnancy also deepens the pigmentation.Nipples and sex
Nipples of both males and females are one of the erogenous zoneErogenous zone
An erogenous zone is an area of the human body that has heightened sensitivity, the stimulation of which may result in the production of erotic sensations or sexual excitement.People have erogenous zones all over their bodies, but which areas are more sensitive than others vary...
s, which are generally stimulated by hands or by mouth during foreplay
Foreplay
In human sexual behavior, foreplay is a set of intimate psychological and physically intimate acts between two or more people meant to create desire for sexual activity and sexual arousal. Either or any of the sexual partners may initiate the foreplay, and they may not be the active partner during...
, which leads to sexual arousal
Sexual arousal
Sexual arousal, or sexual excitement, is the arousal of sexual desire, during or in anticipation of sexual activity. Things that precipitate human sexual arousal are called erotic stimuli, or colloquially known as turn-ons. There are many potential stimuli, both physical or mental, which can cause...
. While female nipples and areolae have been shown to have greater levels of innervation, female nipples are also more sensitive, likely due to hormonal influences as well. During arousal they generally become stiff, erect and protrude out.
The nipple and areola
Areola
This article is about the breast tissue. For the entomology term, see the glossary of Lepidopteran terms. For an artistic cloud motif, see aureola. For the cactus feature, see Areole....
of males and females can be erotic receptors, sometimes intense enough to elicit orgasm
Orgasm
Orgasm is the peak of the plateau phase of the sexual response cycle, characterized by an intense sensation of pleasure...
in some individuals of either sex.
On male mammals
From conception until sexual differentiationSexual differentiation
Sexual differentiation is the process of development of the differences between males and females from an undifferentiated zygote...
, all mammalian fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
es within the same species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
look the same, regardless of sex. In humans, this lasts for around 6 weeks; after which genetically-male fetuses begin producing male hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
s such as testosterone
Testosterone
Testosterone is a steroid hormone from the androgen group and is found in mammals, reptiles, birds, and other vertebrates. In mammals, testosterone is primarily secreted in the testes of males and the ovaries of females, although small amounts are also secreted by the adrenal glands...
. Usually, males' nipples do not change much past this point; however, some males develop a condition known as gynecomastia
Gynecomastia
Gynecomastia or Gynaecomastia, , is the abnormal development of large mammary glands in males resulting in breast enlargement. The term comes from the Greek γυνή gyné meaning "woman" and μαστός mastós meaning "breast"...
, in which the fatty tissue around and under the nipple develops into something similar to a female breast. This may happen whenever the testosterone level drops. Gynecomastia, although not as severe, may occur in pubescent boys undergoing physical changes due to the rapid and uncontrolled release of hormones, including estrogen. The heightened levels of oestrogen in pubescent male bodies leads to the swelling of the nipple and surrounding tissue - this can often look similar to a female human nipple - and may cause slight discomfort.
Thus, because the "female template" is the default for humans, the question is not why evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
has not selected against male nipples, but why it would be advantageous to select against male nipples in the first place:
The uncoupling of male and female traits occurs if there is selection for it: if the trait is important to the reproductive success of both males and females but the best or "optimal" trait is different for a male and a female. We would not expect such an uncoupling if the attribute is important in both sexes and the "optimal" value is similar in both sexes, nor would we expect uncoupling to evolve if the attribute is important to one sex but unimportant in the other. The latter is the case for nipples. Their advantage in females, in terms of reproductive success, is clear. But because the genetic "default" is for males and females to share characters, the presence of nipples in males is probably best explained as a genetic correlation that persists through lack of selection against them, rather than selection for them. Interestingly, though, it could be argued that the occurrence of problems associated with the male nipple, such as carcinomaCarcinomaCarcinoma is the medical term for the most common type of cancer occurring in humans. Put simply, a carcinoma is a cancer that begins in a tissue that lines the inner or outer surfaces of the body, and that generally arises from cells originating in the endodermal or ectodermal germ layer during...
, constitutes contemporary selection against them. In a sense, male nipples are analogous to vestigial structures such as the remnants of useless pelvic bones in whales: if they did much harm, they would have disappeared.In a now-famous paper, Stephen Jay Gould
Stephen Jay GouldStephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation....
and Richard C. Lewontin emphasize that we should not immediately assume that every trait has an adaptive explanation. Just as the spandrelSpandrelA spandrel, less often spandril or splaundrel, is the space between two arches or between an arch and a rectangular enclosure....
s of St. Mark's domed cathedralSt Mark's BasilicaThe Patriarchal Cathedral Basilica of Saint Mark is the cathedral church of the Roman Catholic Archdiocese of Venice, northern Italy. It is the most famous of the city's churches and one of the best known examples of Byzantine architecture...
in VeniceVeniceVenice is a city in northern Italy which is renowned for the beauty of its setting, its architecture and its artworks. It is the capital of the Veneto region...
are simply an architectural consequence of the meeting of a vaulted ceiling with its supporting pillars, the presence of nipples in male mammals is a genetic architectural by-product of nipples in females. So, why do men have nipples? Because females do.
See also
- AreolaAreolaThis article is about the breast tissue. For the entomology term, see the glossary of Lepidopteran terms. For an artistic cloud motif, see aureola. For the cactus feature, see Areole....
- BreastBreastThe breast is the upper ventral region of the torso of a primate, in left and right sides, which in a female contains the mammary gland that secretes milk used to feed infants.Both men and women develop breasts from the same embryological tissues...
- BreastfeedingBreastfeedingBreastfeeding is the feeding of an infant or young child with breast milk directly from female human breasts rather than from a baby bottle or other container. Babies have a sucking reflex that enables them to suck and swallow milk. It is recommended that mothers breastfeed for six months or...
- Intimate partIntimate partAn intimate, personal, or private part is a place on the human body which is customarily kept covered by clothing in public venues and conventional settings, as a matter of decency, decorum, and respectfulness...
- Inverted nippleInverted nippleAn inverted nipple is a condition where the nipple, instead of pointing outward, is retracted into the breast. In some cases, the nipple will be temporarily protruded if stimulated, but in others, the inversion remains regardless of stimulus...
- LactationLactationLactation describes the secretion of milk from the mammary glands and the period of time that a mother lactates to feed her young. The process occurs in all female mammals, however it predates mammals. In humans the process of feeding milk is called breastfeeding or nursing...
- Mammary glandMammary glandA mammary gland is an organ in mammals that produces milk to feed young offspring. Mammals get their name from the word "mammary". In ruminants such as cows, goats, and deer, the mammary glands are contained in their udders...
- MilkMilkMilk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...
- Milk lineMilk lineThe milk lines are two parallel lines, formed by thickenings of the epidermis along the ventral surface of mammals of both sexes. They extend from the upper limbs to the lower limbs and are developed in the embryo...
- Nipple piercingNipple piercingA nipple piercing is a piercing, centered usually at the base of the nipple. It can be pierced at any angle but is usually done horizontally or, less often, vertically. It is also possible to place multiple piercings on top of one another...
- Stimulation of nipples
- Supernumerary (third) nippleSupernumerary nippleA supernumerary nipple is an additional nipple occurring in mammals, including humans...
- UdderUdderAn udder is an organ formed of the mammary glands of female quadruped mammals, especially ruminants such as cattle, goats, sheep and deer. The udder is a single mass hanging beneath the animal, consisting of pairs of mammary glands...