Lactation describes the secretion of milk from the mammary glands, and nursing describes the process of providing breast milk to the young. This process occurs in all female mammals, and in humans it is commonly referred to as breastfeeding. In humans and most species, milk comes out of the mother's nipples.
Babies have a sucking reflex that enables them to suck and swallow milk. Both babies and mothers gain many benefits from breastfeeding. Breast milk is easy to digest and contains antibodies that can protect infants from bacterial and viral infections. Some of the nutrients in breast milk, such as protein and vitamins, help protect an infant against some common childhood illnesses and infections, such as diarrhea, middle ear infections, and certain lung infections. Research indicates that women who breastfeed may have lower rates of certain breast and ovarian cancers.
Colostrum is the first milk produced by the mother during the initial days after giving birth. Colostrum is low in fat and high in carbohydrates, protein, and antibodies to help develop and support the baby's immune system.
Breastfed infants and infants who are fed breast milk have fewer deaths during the first year and experience fewer illnesses than babies fed formulas.
Research also suggests that breast milk contains important fatty acids (building blocks of cells) that help an infant's brain develop. Two specific fatty acids, docosahexaenoic acid (DHA) and arachidonic acid (AA), are components of the brain and are important for developing cognitive skills. Many types of infant formulas available in the United States are fortified with DHA and AA.
While there are conflicting studies about the relative value of artificial feeding, including infant formula, it is acknowledged to be inferior to breastfeeding for both full-term and premature infants. In many countries, artificial feeding is commonly associated with illness and death in infants.
National governments and international organizations, including the World Health Organization (WHO) and the American Academy of Pediatrics (AAP), promote breastfeeding as the best method of feeding infants in their first years of life and beyond. Although breastfeeding is widely regarded as superior to artificial feeding, authorities also encourage the development of safe and improved artificial feeding methods.
Not all the properties of breast milk are understood, but its nutrient content has been well studied. The nutrients in breast milk come from the mother's blood and body. Some studies estimate that in women who exclusively breastfeed, 400-600 extra calories a day are used to produce milk. The water, fat, and nutrient content in breast milk may vary depending on several factors, including the manner in which the baby nurses, the mother's food consumption, and the environment.
Certain medications may pass through the breast milk to the infant when women who are breastfeeding are taking the drugs. Because of the infant's small size and the difference in metabolism between infants and adults, occasionally this transfer of medication can be harmful to the infant. The majority of drugs that are given to breastfeeding women do not cause problems in infants. Questions regarding which drugs are safe to take when breastfeeding should be directed toward a healthcare provider.

Related Terms

Alveoli, ankyloglossia, arachidonic acid, areola, breast, breast feeding, breast milk stimulant, breast pump, candida, candidiasis, cortisol, DHA, docosahexaenoic acid, ejection reflex, estrogen, galactagogue, HPL, human placental lactogen, hypercalcemia, hypoplastic, hypotonia, IgA, immunoglobulin A, insulin, lactation, lactation stimulation, lactogenesis I, lactogenesis II, lactogenesis III, mammary glands, mastitis, milk ejection reflex, nursing, oxytocin, passive immunity, progesterone, prolactin, thrush, thyroxin, tracheo-oesophageal fistula.

causes of lactation

General: Starting in the fourth month of pregnancy, the system in a woman's breast begins to develop. Milk production is affected by several hormones, namely prolactin and oxytocin.
Progesterone: Progesterone levels are increased during pregnancy and drop after birth. This triggers copious milk production by the glands (called alveoli) in the breast lobe (lactating gland) that produces milk.
Estrogen: Estrogen stimulates the milk duct system to mature. Estrogen levels also drop at delivery and remain low for the first several months of breastfeeding. Healthcare professionals recommend that breastfeeding mothers avoid estrogen-based birth control methods, as a spike in exogenous (from outside the body) estrogen levels may reduce a mother's milk supply.
Prolactin: Prolactin contributes to the increased growth of the alveoli during pregnancy.
Oxytocin: Oxytocin causes smooth muscle contraction and causes the uterus to contract around the time of birth. Oxytocin causes the smooth muscle layer of band-like cells surrounding the alveoli to squeeze the newly-produced milk into the duct system. Oxytocin is necessary for the milk ejection reflex and for milk expression to occur.
Human placental lactogen: Human placental lactogen (HPL) is released by the placenta during the second month of pregnancy. HPL appears to aid in breast, nipple, and areola growth before birth.
By the fifth or sixth month of pregnancy, the breasts are ready to produce milk. It is also possible to induce lactation without pregnancy through chemical methods using certain drugs.
Lactogenesis: The process of milk production is called lactogenesis, which is divided into three stages.
Lactogenesis I: During the latter part of pregnancy, the woman's breasts enter into the lactogenesis I stage. This is when the breasts make colostrum (the first milk produced by the mother after birth). At this stage, high levels of progesterone inhibit most milk production. It is not a medical concern if a pregnant woman leaks colostrum before her baby's birth, nor is it an indication of future milk production.
Lactogenesis II: At birth, prolactin levels remain high, while the delivery of the placenta results in a sudden drop in progesterone, estrogen, and HPL levels. This abrupt withdrawal of progesterone in the presence of high prolactin levels stimulates the copious milk production of lactogenesis II.
When the breasts are stimulated, prolactin levels in the blood rise, peak after about 45 minutes, and return to the pre-breastfeeding state about three hours later. The release of prolactin triggers the cells in the alveoli to make milk. Some research indicates that prolactin in milk is higher at times during the milk production process, and that the highest levels tend to occur between 2 a.m. and 6 a.m.
Other hormones, notably insulin, thyroxine (thyroid hormone), and cortisol (the stress hormone), are also produced during lac II, but their roles are not yet well understood. Although biochemical markers indicate that lactogenesis II begins within 30-40 hours of birth, mothers do not typically begin feeling increased breast fullness until two to three days after birth.
Colostrum is the first milk secreted or produced by the breast. It contains higher amounts of white blood cells and antibodies than mature milk. Antibodies are proteins made by the immune system to fight foreign substances, such as bacteria or viruses, in the body. Colostrum is especially high in immunoglobulin A (IgA) class of antibodies. These antibodies coat the lining of the baby's immature intestines and help prevent germs from invading the baby's system. Secretory IgA also helps prevent food allergies. During the first two weeks after the birth, colostrum production slowly gives way to mature breast milk.
Lactogenesis III: The hormonal endocrine control system aids in milk production during pregnancy and the first few days after the birth. When the milk supply is more firmly established, the autocrine (or local) control system begins. This stage is called lactogenesis III. During this stage, the more that milk is removed from the breasts, the more the breast will produce milk. Draining the breasts more fully also increases the rate of milk production, thus the milk supply is strongly influenced by how often the baby feeds and how well the mother is able to transfer milk from the breast. Low milk supply can often be traced to: not feeding or pumping often enough; inability of the infant to transfer milk effectively caused by jaw or mouth structure deficits or poor latching technique; rare maternal endocrine disorders; hypoplastic breast tissue; a metabolic or digestive inability in the infant, making the baby unable to digest the milk he/she receives; and inadequate calorie intake or malnutrition of the mother.
Milk ejection reflex: The release of the hormone oxytocin leads to the milk ejection or let-down reflex. Oxytocin stimulates the muscles surrounding the breast to squeeze out the milk. Breastfeeding mothers describe the sensation differently. Some feel a slight tingling, others feel immense amounts of pressure or slight pain/discomfort, and still others do not feel any difference.
The milk ejection reflex is not always consistent. Stress or anxiety can cause difficulties with breastfeeding. The thought of breastfeeding or the sound of any baby can stimulate this reflex, causing unwanted leakage Also, both breasts may give out milk when an infant is feeding from one breast. However, these problems often subside after two weeks of feeding.
A poor milk ejection reflex can be due to sore or cracked nipples, separation from the infant, a history of breast surgery, or tissue damage from prior breast trauma. If a mother has trouble breastfeeding, different methods of assisting the milk ejection reflex may help. These include feeding in a familiar and comfortable location, massage of the breast or back, or warming the breast with a cloth or shower.
Afterpains: Afterpains occur with increased levels of the hormone oxytocin. Oxytocin triggers the milk ejection reflex and also causes the uterus to contract. These pains may range from period-like cramps to strong labor-like contractions. The afterpains can be more severe with second and subsequent babies.
Lactation without pregnancy: It is also possible to induce lactation without pregnancy. Women who have never been pregnant are sometimes able to induce enough lactation to breastfeed. This is called "induced lactation." A woman who has breastfed before and re-starts is said to "relactate." If the nipples of a non-pregnant woman are consistently stimulated by a breast pump or actual suckling, the breasts will eventually begin to produce enough milk to begin feeding a baby. Once established, lactation adjusts according to demand. This is how some adoptive mothers, usually beginning with a supplemental nursing system or some other form of supplementation, are able to breastfeed. There is thought to be little or no difference in milk composition whether lactation is induced or a result of pregnancy.
Also, rare accounts of male lactation may occur. Some drugs, primarily atypical antipsychotics such as risperidone (Risperdal®), may cause lactation in both women and men.


Healthcare professionals recommend the following techniques for breastfeeding:
With a free hand, place the thumb on top of the breast and the other fingers below the breast. Do not touch the areola (the dark skin around the nipple). The areola is where the baby's lips will be.
Touch the baby's lips with the nipple until the baby opens his or her mouth very wide. Put the nipple all the way in the baby's mouth and pull the baby's body close. This lets the baby's jaw squeeze the milk ducts under the areola.
When the baby is "latched on" the right way, both lips should pout out (not be pulled in over his or her gums) and cover nearly all of the areola. Instead of smacking noises, the baby will make low-pitched swallowing noises. The baby's jaw may move back and forth. If pain is felt while the baby is nursing, he or she is probably not latched on correctly.
The baby's nose may be touching the breast during nursing. Babies' noses are designed to allow air to get in and out in just such a case. But if the individual is concerned that the baby cannot breathe easily, they can gently press down on the breast near the baby's nose to give him or her more room to breathe.
Holding the baby: A baby can be held in a number of ways during breastfeeding. The baby should not have to turn his or her head or strain his or her neck to nurse. In the cradle position, put the baby's head in the crook of the arm. Support the baby's back and bottom with the arm and hand. The baby will be lying sideways facing the individual. The mother's breast should be right in front of the baby's face.
The football position consists of tucking the baby under the arm like a football with his or her head resting on the hand. Support the baby's body with the forearm. This may be a good position if the mother is recovering from a cesarean section or if the baby is very small.
Mothers can also lie on their side with the baby facing the breast. Pillows can be used to prop up the mother's head and shoulders. This is also a good position if the mother is recovering from a cesarean section or an episiotomy.
Milk ejection reflex: A few seconds to several minutes after the breastfeeding is started, the mother may feel a tingle in her breast, and milk may start to drip from the breast not being used. These are signs that the milk is ready to flow.
This milk ejection reflex makes breastfeeding easier for the baby. Let-down may also occur if a feeding is overdue, if the mother hears the baby cry, or even while the mother is thinking about the baby.
Milk ejection can be forceful enough to cause the baby to cough. If this is a problem, the mother can express some of her milk by hand before a feeding to bring on the ejection reflex before starting breastfeeding.
Feeding frequency: Feed the baby as often as he or she wants to be fed. This may be eight to 12 times a day or more. How often a baby wants to feed may change over time as he or she goes through growth spurts. Growth spurts occur at about two and six weeks of age and again at about three and six months of age.
Let the baby nurse until he or she is satisfied. This may be for about 15-20 minutes at each breast. Try to have the baby nurse from both breasts at each feeding. Signs that the baby is getting enough milk include: acts satisfied after each feeding and gains weight constantly after the first three to seven days after birth (the baby may lose a little weight during the first week after being born); have about six to eight wet diapers a day; and have about two to five or more stools a day at first. After the first week, the infant may then have two or less stools a day. Stools will be runny at first. If the mother is nursing fewer than eight times a day, it is especially important to be aware of these signs.
Increasing milk supply: If the baby needs more milk, increase the number of feedings a day. It is also important for the mother to get plenty of rest, eat a healthy, well-balanced diet, and drink plenty of fluids. Giving the body time to catch up to the baby's demands is important to producing enough milk.
Before breastfeeding, mothers can put a warm compress over the breasts for about 15 minutes to increase milk flow. Alternatively, patients can take warm showers and/or gently massage the breasts to increase milk flow. Do not start giving the baby formula or cereal. If formula or cereal is given to the baby, he or she may not want as much breast milk. This will decrease the mother's milk supply. Also, the baby does not need any solid foods until he or she is four to six months old.
Diet: The best diet for a breastfeeding woman is well-balanced and has plenty of calcium. Eating fresh fruits and vegetables, whole-grain cereals and breads, meats or beans, and milk and dairy foods like cheese is recommended by healthcare professionals. The mother will need to get enough calories - about 500 more per day than usual. The mother will also need to drink plenty of fluids.
A balanced diet that includes five servings of milk or dairy products each day will give the mother enough calcium. If the mother does not eat meat or dairy products, the calcium needed can be obtained from broccoli, sesame seeds, tofu (soy), and kale. Also, calcium supplementation is available. A doctor or healthcare provider can help the mother with dietary issues.
If foods bother the baby, it is recommended by healthcare professionals to stop eating the food causing a problem. Caffeine and alcohol can get into the mother's milk, so mothers should limit these substances. Drugs, including non-prescription and prescription items, can also get into the mother's milk. It is best not to take anything without talking to a doctor first. Also, if the mother smokes, nursing is another good reason to try to quit. Smoking can cause the mother to make less milk and the chemicals in cigarettes and smoke can get into the milk.


Breast pumps: If a mother is breastfeeding her baby, a breast pump may offer flexibility. Breastfeeding is a round-the-clock commitment. That is why many breastfeeding mothers consider breast pumps very important. Breast pumps help express the milk from the mother's breast. Some breast pumps are hand-operated, others run on electricity, and the designs vary. Some models attach to only one breast while others let the mother express milk from both breasts at once.
Choosing a breast pump depends on several factors. These factors include how often the breast pump is to be used. A simple hand pump works best on occasion, and an electric pump works best when a mother works full-time or is away from the baby for more than a few hours a day. Electric pumps stimulate the breasts more effectively than hand pumps. This helps empty the breasts and protect the milk supply. Electric breast pumps are faster than manual pumps. Double breast pumps allow pumping both breasts and help stimulate milk production while cutting pumping time in half.
Every pump has a shield to place over the breast. If the mother is concerned that the standard breast shield is too small, check with individual manufacturers about other options. If the mother wants to pump both breasts at once, make sure the pump is equipped with two breast shields.
Preparing and storing breast milk: When preparing breast milk, it is recommended by healthcare professionals to be sure to wash the hands before expressing or handling breast milk and when collecting milk, be sure to store it in clean containers, such as screw cap bottles, hard plastic cups with tight caps, or heavy-duty bags that fit directly into nursery bottles. Avoid using ordinary plastic storage bags or formula bottle bags, as these could easily leak or spill; if delivering breast milk to a child care provider, clearly label the container with the child's name and date; clearly label the milk with the date it was expressed to facilitate using the oldest milk first; do not add fresh milk to already frozen milk within a storage container as it is best not to mix the two; and do not save milk from a used bottle for use at another feeding.
Thawing breast milk: As time permits, thaw frozen breast milk by transferring it to the refrigerator for thawing or by swirling it in a bowl of warm water. Healthcare professionals warn against using a microwave oven to thaw or heat bottles of breast milk as they do not heat liquids evenly. Uneven heating could easily scald a baby or damage the milk. Bottles may explode if left in the microwave too long. Excess heat can destroy the nutrient quality of the expressed milk.
Breast milk can be stored at room temperature for four to eight hours (at no warmer than 77 degrees Fahrenheit, or 25 degrees Celsius). Breast milk can be stored in the refrigerator for up to eight days at 32-39 degrees Fahrenheit (0 to 3.9 degrees Celsius). Breast milk can be stored in the freezer: for up to two weeks in a freezer compartment located inside the refrigerator; for three to four months in a freezer that is self-contained and connected on top of or on the side of the refrigerator; or for six months or more in a deep freezer that is always 0 degrees Fahrenheit (-17.8 degrees Celsius). It is important to leave about an inch of space at the top of the container or bottle to allow for expansion of the milk when it freezes. If the breast milk is thawed, it can be refrigerated and used within 24 hours, but it is important not to refreeze it.