Some women (approximately 15%) will require antibiotic treatment for infection which is usually caused by bacteria from the skin or the baby's mouth that entering the milk ducts through skin lesions of the nipple or through the opening of the nipple. Infection is usually caused by "staphylococcus aureus". Infectious pathogens commonly associated with mastitis are "Staphylococcus aureus", "streptococcus" spp., gram-negative bacilli such as "Escherichia coli". "Salmonella spp.", mycobacteria, "candida", and Cryptococcus have been identified in rare instances.

Recent research suggests that infectious pathogens play a much smaller role in the pathogenesis than was commonly assumed only a few years ago. Most detected pathogens are very common species that are natural part of the breast fauna and simple detection of their presence is not sufficient to prove a causative role. Furthermore, there are indications that treatment with antibiotics may have minimal impact, and over-all there is insufficient evidence to confirm or refute the effectiveness of antibiotic therapy for treating lactational mastitis.

When it occurs in breastfeeding mothers, it is known as puerperal mastitis, lactation mastitis, or lactational mastitis. When it occurs in non breastfeeding women it is known as non-puerperal or nonlactational. Mastitis can, in rare cases, occur in men. Inflammatory breast cancer has symptoms very similar to mastitis and must be ruled out.

The symptoms are similar for puerperal and nonpuerperal mastitis but predisposing factors and treatment can be very different.

"Duct ectasia" in the literal sense (literally: duct widening) is a very common and thus rather unspecific finding, increasing with age. However, in the way in which the term is mostly used, duct ectasia is an inflammatory condition of the larger-order lactiferous ducts. It considered likely that the condition is associated with aseptic (chemical) inflammation related to the rupture of ducts or cysts. It is controversial whether duct dilation occurs first and leads to secretory stasis and subsequent periductal inflammation or whether inflammation occurs first and leads to an inflammatory weakening of the duct walls and then stasis. When the inflammation is complicated by necrosis and secondary bacterial infection, breast abscesses may form. Subareolar abscess, also called Zuska's disease (only nonpuerperal case), is a frequently aseptic inflammation and has been associated with squamous metaplasia of the lactiferous ducts.

The duct ectasia—periductal mastitis complex affects two groups of women: young women (in their late teens and early 20s) and perimenopausal women. Women in the younger group mostly have inverted nipples due to squamous metaplasia that lines the ducts more extensively compared to other women and produces keratin plugs which in turn lead to duct obstruction and then duct dilation, secretory stasis, inflammation, infection and abscess. This is not typically the case for women in the older group; in this group, there is likely a multifactorial etiology involving the balance in estrogen, progesterone and prolactin.

Treatment of mastitis and/or abscess in nonlactating women largely the same as that of lactational mastitis, generally involving antibiotics treatment, possibly surgical intervention by means of fine-needle aspiration and/or incision and drainage and/or interventions on the lactiferous ducts (for details, "see also" the articles on treatment of mastitis, of breast abscess and of subareolar abscess). Additionally, an investigation for possible malignancy is needed, normally by means of mammography, and a pathological investigation such as a biopsy may be necessary to exclude malignant mastitis. Although no "causal" relation with breast cancer has been established, there appears to be an increased statistical risk of breast cancer, warranting a long-term surveillance of patients diagnosed with non-puerperal mastitis.

Nonpuerperal breast abscesses have a higher rate of recurrence compared to puerperal breast abscesses. There is a high statistical correlation of nonpuerperal breast abscess with diabetes mellitus (DM). On this basis, it has recently been suggested that diabetes screening should be performed on patients with such abscess.

90% of cases are smokers, however only a very small fraction of smokers appear to develop this lesion. It has been speculated that either the direct toxic effect or hormonal changes related to smoking could cause squamous metaplasia of lactiferous ducts. It is not well established whether the lesion regresses after smoking cessation.

Extrapuerperal cases are often associated with hyperprolactinemia or with thyroid problems. Also diabetes mellitus may be a contributing factor in nonpuerperal breast abscess.

The term nonpuerperal mastitis describes inflammatory lesions of the breast (mastitis) that occur unrelated to pregnancy and breastfeeding.

It is sometimes equated with duct ectasia, but other forms can be described.

Also called Zuska's disease (only nonpuerperal case), subareolar abscess is a subcutaneous abscess of the breast tissue beneath the areola of the nipple. It is a frequently aseptic inflammation and has been associated with squamous metaplasia of lactiferous ducts.

The term is usually understood to include breast abscesses located in the retroareolar region or the periareolar region, but not those located in the periphery of the breast.

Subareolar abscess can develop both during lactation or extrapuerperal, the abscess is often flaring up and down with repeated fistulation.

Mastitis is most often transmitted by repetitive contact with the milking machine, and through contaminated hands or materials.

Another route is via the oral-to-udder transmission among calves. Feeding calves on milk may introduce some mastitis causing bacteria strain in the oral cavity of the calf where it will stay dormant until it is transmitted elsewhere. Since grouped calves like to stimulate suckling, they will transmit the bacteria to the udder tissue of their fellow calves. The bacteria will lay dormant in the udder tissue as the calf grows until it begins to lactate. That is when the bacteria activates and causes mastitis. This calls for strict calf management practices to curb this route of transmission.

Breast cancer risk is elevated for defined fraction of lesions. Except for patients with a strong family history of breast cancer, where the risk is two-fold, nonproliferative lesions have no increased risk. Proliferative lesions also have approximately a 2-fold risk. In particular, atypical hyperplasia is associated with an increased risk of developing breast cancer. Atypical lobular hyperplasia is associated with the greatest risk, approximately 5-fold and especially high relative risk of developing premenopausal breast cancer. Atypical ductal hyperplasia is associated with 2.4-fold risk. In contrast, a New England Journal of Medicine article states that for women with a strong familial history of breast cancer, the risk of future breast cancer is roughly doubled, independent of histological status. The article further states "The relative risk of breast cancer for the cohort was 1.56 (95 percent confidence interval, 1.45 to 1.68), and this increased risk persisted for at least 25 years after biopsy. The relative risk associated with atypia was 4.24 (95 percent confidence interval, 3.26 to 5.41), as compared with a relative risk of 1.88 (95 percent confidence interval, 1.66 to 2.12) for proliferative changes without atypia and of 1.27 (95 percent confidence interval, 1.15 to 1.41) for nonproliferative lesions. The strength of the family history of breast cancer, available for 4808 women, was a risk factor that was independent of histologic findings. No increased risk was found among women with no family history and nonproliferative findings. In the first 10 years after the initial biopsy, an excess of cancers occurred in the same breast, especially in women with atypia."

It is not well understood whether the lesions are precursors of breast cancer or only indication of increased risk, for most types of lesions the chance of developing breast cancer is nearly the same in the affected and unaffected breast (side) indicating only coincidence of risk factors. For atypical lobular hyperplasia there is high incidence of ipsilateral breast cancers indicating a possible direct carcinogenetic link.

The cause is currently unknown. The histology is suggestive of an autoimmune reaction. The high rate of relapses as well as relatively high proportion of bilateral cases is highly suggestive of a systemic predisposition.

Presently most evidence points towards an important role of elevated prolactin levels or overt hyperprolactinemia with additional triggers such as local trauma or irritation. Alpha 1-antitrypsin deficiency was documented in one case, interferon-alpha therapy in another case. Similar cases of granulomatous mastitis were reported in IgG4-related disease though the exact relationship to IGM remains to be elucidated. Other contributing factors of IGM were investigated such as oral contraceptives usage. Many cases were reported after use of prolactin elevating medications such as antipsychotics.

Elevated prolactin levels have the direct effects of increasing secretory activity of breast lobules, maintaining tight junctions of the ductal epithelium, preventing involution of the breast gland after weaning and are known to stimulate the immune system, contributing to both physiological and pathological granulomatous lesions and non-caseating granulomas. PRL is also secreted locally in the breast and local secretion by lymphocytes may be enhanced during inflammatory reactions.

Autoimmune reaction to extravasated fat and protein rich luminal fluid (denaturized milk) resulting from the secretory activity is assumed to be one of the triggers of IGM. Several other hormones can contribute to PRL signaling in the breast gland, high levels of insulin caused for example by peripheral insulin resistance (resulting from pregnancy, gestational diabetes or developing diabetes mellitus type 2) will enhance the galactogenic and antiapoptotic effects of PRL and growth hormone by acting synergistically with IGF-1.

Mastitis occurs when white blood cells (leukocytes) are released into the mammary gland, usually in response to bacteria invading the teat canal. Milk-secreting tissue and various ducts throughout the mammary gland are damaged due to toxins released by the bacteria. Mastitis can also occur as a result of chemical, mechanical, or thermal injury.

Some women who have pain in one or both breasts may fear breast cancer. However, breast pain is not a common symptom of cancer. The great majority of breast cancer cases do not present with symptoms of pain, though breast pain in older women is more likely to be associated with cancer.

Duct ectasia of the breast or mammary duct ectasia or plasma cell mastitis is a condition in which the lactiferous duct becomes blocked or clogged. This is the most common cause of greenish discharge.

Mammary duct ectasia can mimic breast cancer. It is a disorder of peri- or post-menopausal age.

"Duct ectasia syndrome" is a synonym for nonpuerperal mastitis but the term has also been occasionally used to describe special cases of fibrocystic diseases, mastalgia or as a wastebasket definition of benign breast disease.

Correlation of duct widening with the "classical" symptoms of duct ectasia syndrome is unclear. However, duct widening was recently very strongly correlated with noncyclic breast pain.

Duct diameter is naturally variable, subject to hormonal interactions. Duct ectasia syndrome in the classical meaning is associated with additional histological changes.

Idiopathic granulomatous mastitis is defined as granulomatous mastits without any other attributable cause such as those above mentioned. It occurs on average two years and almost exclusively up to six years after pregnancy, usual age range is 17 to 42 years. Some cases have been reported that were related to drug induced hyperprolactinemia.

Exceptionally rarely it has been diagnosed during pregnancy and in men.

The term has several meanings on histological and symptomatic levels and on both levels "usage" overlaps with mastalgia, fibrocystic disease and specific sub- or superclasses of nonpuerperal mastitis. While this is not ideal for a definition it results from actual usage in international literature. Because research literature regarding duct ectasia is anything but abundant it is probably easiest to determine the exact meaning(s) intended by the respective authors on a case by case basis and this section can offer only a few hints.

Typical usage in North America is a synonym of nonpuerperal mastitis, including the special cases of granulomatous mastitis, comedo mastitis, subareolar abscess with or without squamous metaplasia of lactiferous ducts and fistulation.

Simple duct widening should be carefully distinguished from more complex histological changes.

Among women worldwide, breast cancer is the most common cause of cancer death. Breast self-examination (BSE) is an easy but unreliable method for finding possible breast cancer. Factors that appear to be implicated in decreasing the risk of, early diagnosis of. or recurrence of breast cancer are regular breast examinations by health care professionals, regular mammograms, self-examination of breasts, healthy diet, and exercise to decrease excess body fat.

Breast diseases can be classified either with disorders of the integument, or disorders of the reproductive system. A majority of breast diseases are noncancerous.

There are usually no adverse side effects to this condition. In almost all cases it subsides after menopause. A possible complication arises through the fact that cancerous tumors may be more difficult to detect in women with fibrocystic changes.

The most common causes of nipple inversion include:

- Born with condition

- Trauma which can be caused by conditions such as fat necrosis, scars or it may be a result of surgery

- Breast sagging, drooping or ptosis

- Breast cancer

- breast carcinoma

- Paget's disease

- Inflammatory Breast Cancer (IBC)

- Breast infections or inflammations

- mammary duct ectasia

- breast abscess

- mastitis

- Genetic variant of nipple shape such as

- Weaver syndrome

- congenital disorder of glycosylation type 1A & 1 L

- Kennerknecht-Sorgo-Oberhoffer syndrome

- Gynecomastia

- Holoprosencephaly, recurrent infections and monocytosis

- Tuberculosis

Around 10–20% of all women are born with this condition. Most common nipple variations that women are born with are caused by short ducts or a wide areola muscle sphincter.

Inverted nipples can also occur after sudden and major weight loss.

In a survey in New York city 35% of nursing mothers stopped breastfeeding after one week due to the pain of cracked nipples. Thirty percent stopped breastfeeding between weeks one and three. Another survey of breastfeeding mothers in Brazil reported that there was 25% higher risk of interruption of exclusive breastfeeding when the women had cracked nipples. Mothers with higher education levels are more likely to continue breastfeeding despite the pain of cracked nipples.

The clinical management of a cyst of Montgomery depends upon the symptoms of the patient.

If there are no signs of infection, a cyst of Montgomery can be observed, because more than 80% resolve spontaneously, over only a few months. However, in some cases, spontaneous resolution may take up two years. In such cases, a repeat ultrasonography may become necessary. If, however, the patient has signs of an infection, for example reddening (erythema), warmth, pain and tenderness, a treatment for mastitis can be initiated, which may include antibiotics and non-steroidal anti-inflammatory drugs (NSAIDs). With treatment, inflammatory changes usually disappear quickly. In rare cases, drainage may become necessary. A surgical treatment of a cyst of Montgomery, i.e. a resection, may become necessary only if a cyst of Montgomery persists, or the diagnosis is questioned clinically.

The prognosis seems to be excellent. In one series, all adolescent patients with a cyst of Montgomery had a favourable outcome.

The importance of preventing cracked nipples while breastfeeding has been reported. In an informal survey of breastfeeding in the UK, some mothers reported that they stopped breastfeeding because the cracked nipples made it too painful.

Cyclical breast pain (cyclical mastalgia) is often associated with fibrocystic breast changes or duct ectasia and thought to be caused by changes of prolactin response to thyrotropin. Some degree of cyclical breast tenderness is normal in the menstrual cycle, and is usually associated with menstruation and/or premenstrual syndrome (PMS).

Noncyclical breast pain has various causes and is harder to diagnose. Noncyclical pain has frequently its root cause outside the breast. Some degree of non-cyclical breast tenderness can normally be present due to hormonal changes in puberty (both in girls and boys), in menopause and during pregnancy. After pregnancy, breast pain can be caused by breastfeeding. Other causes of non-cyclical breast pain include alcoholism with liver damage (likely due to abnormal steroid metabolism), mastitis and medications such as digitalis, methyldopa (an antihypertensive), spironolactone, certain diuretics, oxymetholone (an anabolic steroid), and chlorpromazine (a typical antipsychotic). Also, shingles can cause a painful blistering rash on the skin of the breasts.

It occurs in all adult age groups. While the majority of patients are between 40 and 59 years old, age predilection is much less pronounced than in noninflammatory breast cancer. The overall rate is 1.3 cases per 100000, black women (1.6) have the highest rate, Asian and Pacific Islander women the lowest (0.7) rates.

Most known breast cancer risk predictors do not apply for inflammatory breast cancer. It may be slightly associated with cumulative breast-feeding duration.

The periareolar glands of Montgomery in the breast are also called Montgomery tubercles or Morgagni tubercles. These periareolar glands are small, papular tissue projections at the edge of the areola (nipple).

Obstruction of the Montgomery tubercles may result in an acute inflammation, a clear or light brownish fluid may drain out of the areola (nipple discharge), and an subareolar mass may develop, the cyst of Montgomery.

Failure to remove breast milk, especially in the first few days after delivery when the milk comes in and fills the breast, and at the same time blood flow to the breasts increases, causing congestion. The common reasons why milk is not removed adequately are delayed initiation of breastfeeding, infrequent feeds, poor attachment, ineffective suckling., a sudden change in breastfeeding routine, suddenly stopping breastfeeding, or if your baby suddenly starts breastfeeding less than usual.