The duct widening is commonly believed to be a result of secretory stasis, including stagnant colostrum, which also causes periductal inflammation and fibrosis. However, because nonspecific duct widening is common it might be also coincidental finding in many processes.

Smokers seem more often affected by duct ectasia "syndrome" although the reported results are not entirely consistent. The correlation with smoking status appears weaker than for subareolar abscess. Correlation with the actual duct widening is not known.

Both duct widening and duct ectasia syndrome are frequently bilateral, hence systemic causes are likely involved.

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.

Extramammary Paget's disease is usually seen in isolation and is associated with an underlying invasive malignancy about 12% of the time. It is associated with an underlying adnexal malignancy about 24% of the time. Paget's disease of the breast is almost always associated with an underlying invasive malignancy, i.e. breast cancer (e.g. mammary ductal carcinoma).

It is likely that this syndrome is inherited in an autosomal dominant fashion, however there may be a recessive form with hypotonia and developmental delay.

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 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.

Scalp–ear–nipple syndrome (also known as "Finlay–Marks syndrome") is a condition associated with aplasia cutis congenita.

Paget's disease of the vulva, a rare disease, may be a primary lesion or associated with adenocarcinoma originating from local organs such as the Bartholin gland, the urethra, or the rectum and thus be secondary. Patients tend to be postmenopausal.

Paget's disease of the penis may also be primary or secondary, and is even rarer than genital Paget’s disease in women. At least one case has been misdiagnosed as Bowen's disease. Isolated Paget's disease of the penis is extremely rare.

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.

A cyst of Montgomery is a benign breast mass, usually found in adolescent girls. Typically, it resolves spontaneously by itself.

Nipple adenomas most commonly occur in 30- to 40-year-old women, but can also occur in men. They can also occur at any age, including in the elderly, in adolescence, and in infants.

Ulnar–mammary syndrome or Schinzel syndrome is a cutaneous condition characterized by nipple and breast hypoplasia or aplasia.

It has been associated with TBX3.

A nipple adenoma is a rare benign tumour of the breast.

The condition may also be known as :

Genital leiomyomas (also known as "Dartoic leiomyomas") are leiomyomas that originate in the dartos muscles of the genitalia, areola, and nipple.

Squamous metaplasia of lactiferous ducts - abbreviated SMOLD is a change where the normal double layer cuboid epithelium of the lactiferous ducts is replaced by squamous keratinizing cell layers. The resulting epithelium is very similar to normal skin, hence some authors speak of epidermalization. SMOLD is rare in premenopausal women (possibly 0.1-3%) but more frequent (possibly up to 25%) in postmenopausal women where it does not cause any problems at all.

SMOLD appears to be a completely benign lesion and may exist without causing any symptoms. In principle it ought to be completely reversible as the classification as metaplasia would suggest. Because of difficulties in observing the actual changes and rare incidence of the lesion this does not appear to be documented.

The last section of the lactiferous ducts is always lined with squamous keratinizing epithelium which appears to have important physiological functions. For example, the keratin forms plugs sealing the duct entry and has bacteriostatic properties. In SMOLD the keratinizing lining which is supposed to form only the ends of the lactiferous ducts extends deep into the ducts.

SMOLD is distinct from squamous metaplasia that may occur in papilomatous hyperplasia. It is believed to be unrelated to squamous cell carcinoma of the breast which probably arises from different cell types.

The keratin plugs (debris) produced by SMOLD have been proposed as the cause for recurrent subareolar abscesses by causing secretory stasis. The epidermalized lining has also different permeability than the normal lining, hindering resorption of glandular secretions. The resorption is necessary to dispose of stalled secretions inside the duct - and at least equally important it affects osmotic balance which in turn is an important mechanism in the control of lactogenesis (this is relevant both in puerperal and nonpuerperal mastitis).

While in lactating women this would appear to be a very plausible pathogenesis, there is some uncertainty about the pathogenesis in non-lactating women where breast secretions should be apriori minimal. It appears pathologic stimulation of lactogenesis must be present as well to cause subareolar abscess and treatment success with bromocriptin appears to confirm this as compared to poor success rate of the usual antibiotic and surgical treatments documented by Hanavadi et al.

Further uncertainty in the relation of SMOLD and the subareolar abscess is that squamous metaplasia is very often caused by inflammatory processes. SMOLD could be the cause of the inflammation – or the result of a previous or longstanding inflammation.

SMOLD usually affects multiple ducts and frequently (relative to extremely low absolute prevalence) both breasts hence it is very likely that systemic changes such as hormonal interactions are involved.

At least the following factors have been considered in the aetiology of SMOLD: reactive change to chronic inflammation, systemic hormonal changes, smoking, dysregulation in beta-catenin expression, changes in retinoic acid and vitamin D metabolism or expression.

Vitamin A deficiency may cause epidermilization of the ducts and squamous metaplasia and likely also contributes to infection. Vitamin A deficiency has been observed to cause squamous metaplasia in many types of epithelia. However supplementation with Vitamin A would be beneficial only in exceptional cases because normally the local catabolism of vitamin A will be the regulating factor.

Squamous metaplasia of breast epithelia is known to be more prevalent in postmenopausal women (where it does not cause any problems at all). Staurosporine, a nonspecific protein kinase C inhibitor can induce squamous metaplasia in breast tissue while other known PKC inhibitors did not show this effect. cAMP stimulation can also induce squamous metaplasia.

OPA has been found in most countries where sheep are farmed, with the exception of Australia and New Zealand. OPA has been eradicated in Iceland.

No breed or sex of sheep appears to be predisposed to OPA. Most affected sheep show signs at 2 to 4 years of age.

OPA is not a notifiable disease, and therefore it is difficult to assess its prevalence.

Intraductal papillomas of the breast are benign lesions with an incidence of approximately 2-3% in humans.

Two types of intraductal papillomas are generally distinguished. The central type develops near the nipple. They are usually solitary and often arise in the period nearing menopause. On the other hand, the peripheral type are often multiple papillomas arising at the peripheral breasts, and are usually found in younger women. The peripheral type are associated with a higher risk of malignancy.

They are the most common cause of bloody nipple discharge in women age 20-40 and generally do not show up on mammography due to their small size. They may be detectable on ultrasound. A galactogram is the most definitive test but is somewhat invasive.

The masses are often too small to be palpated or felt. A galactogram is therefore necessary to rule out the lesion.

Excision is sometimes performed. Microdochectomy/microdochotomy (removal of a breast duct) is the treatment of choice.

PUNLMPs can lead to blood in the urine (hematuria) or may be asymptomatic.

Among those in the intensive care unit, ulceration resulting in bleeding is very rare.

A papilloma (plural papillomas or papillomata) ("" + "") is a benign epithelial tumor growing exophytically (outwardly projecting) in nipple-like and often finger-like fronds. In this context refers to the projection created by the tumor, not a tumor on an already existing papilla (such as the nipple).

When used without context, it frequently refers to infections (squamous cell papilloma) caused by human papillomavirus (HPV), such as warts. Human papillomavirus infection is a major cause of cervical cancer, although most HPV infections do not cause cancer. There are, however, a number of other conditions that cause papilloma, as well as many cases in which there is no known cause.

In urologic pathology, PUNLMP, short for papillary urothelial neoplasm of low malignant potential, is an exophytic (outward growing), (microscopically) nipple-shaped (or papillary) pre-malignant growth of the lining of the upper genitourinary tract (the urothelium), which includes the renal pelvis, ureters, urinary bladder and part of the urethra.

"PUNLMP" is pronounced "pun"-"lump", like the words "pun" and "lump".

As their name suggests, PUNLMPs are neoplasms, i.e. clonal cellular proliferations, that are thought to have a low probability of developing into urothelial cancer, i.e. a malignancy such as bladder cancer.

Many conditions affect the human integumentary system—the organ system covering the entire surface of the body and composed of skin, hair, nails, and related muscle and glands. The major function of this system is as a barrier against the external environment. The skin weighs an average of four kilograms, covers an area of two square meters, and is made of three distinct layers: the epidermis, dermis, and subcutaneous tissue. The two main types of human skin are: glabrous skin, the hairless skin on the palms and soles (also referred to as the "palmoplantar" surfaces), and hair-bearing skin. Within the latter type, the hairs occur in structures called pilosebaceous units, each with hair follicle, sebaceous gland, and associated arrector pili muscle. In the embryo, the epidermis, hair, and glands form from the ectoderm, which is chemically influenced by the underlying mesoderm that forms the dermis and subcutaneous tissues.

The epidermis is the most superficial layer of skin, a squamous epithelium with several strata: the stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale. Nourishment is provided to these layers by diffusion from the dermis, since the epidermis is without direct blood supply. The epidermis contains four cell types: keratinocytes, melanocytes, Langerhans cells, and Merkel cells. Of these, keratinocytes are the major component, constituting roughly 95 percent of the epidermis. This stratified squamous epithelium is maintained by cell division within the stratum basale, in which differentiating cells slowly displace outwards through the stratum spinosum to the stratum corneum, where cells are continually shed from the surface. In normal skin, the rate of production equals the rate of loss; about two weeks are needed for a cell to migrate from the basal cell layer to the top of the granular cell layer, and an additional two weeks to cross the stratum corneum.

The dermis is the layer of skin between the epidermis and subcutaneous tissue, and comprises two sections, the papillary dermis and the reticular dermis. The superficial papillary dermis with the overlying rete ridges of the epidermis, between which the two layers interact through the basement membrane zone. Structural components of the dermis are collagen, elastic fibers, and ground substance. Within these components are the pilosebaceous units, arrector pili muscles, and the eccrine and apocrine glands. The dermis contains two vascular networks that run parallel to the skin surface—one superficial and one deep plexus—which are connected by vertical communicating vessels. The function of blood vessels within the dermis is fourfold: to supply nutrition, to regulate temperature, to modulate inflammation, and to participate in wound healing.

The subcutaneous tissue is a layer of fat between the dermis and underlying fascia. This tissue may be further divided into two components, the actual fatty layer, or panniculus adiposus, and a deeper vestigial layer of muscle, the panniculus carnosus. The main cellular component of this tissue is the adipocyte, or fat cell. The structure of this tissue is composed of septal (i.e. linear strands) and lobular compartments, which differ in microscopic appearance. Functionally, the subcutaneous fat insulates the body, absorbs trauma, and serves as a reserve energy source.

Conditions of the human integumentary system constitute a broad spectrum of diseases, also known as dermatoses, as well as many nonpathologic states (like, in certain circumstances, melanonychia and racquet nails). While only a small number of skin diseases account for most visits to the physician, thousands of skin conditions have been described. Classification of these conditions often presents many nosological challenges, since underlying etiologies and pathogenetics are often not known. Therefore, most current textbooks present a classification based on location (for example, conditions of the mucous membrane), morphology (chronic blistering conditions), etiology (skin conditions resulting from physical factors), and so on. Clinically, the diagnosis of any particular skin condition is made by gathering pertinent information regarding the presenting skin lesion(s), including the location (such as arms, head, legs), symptoms (pruritus, pain), duration (acute or chronic), arrangement (solitary, generalized, annular, linear), morphology (macules, papules, vesicles), and color (red, blue, brown, black, white, yellow). Diagnosis of many conditions often also requires a skin biopsy which yields histologic information that can be correlated with the clinical presentation and any laboratory data.

Most patients diagnosed with Paget's disease of the nipple are over age 50, but rare cases have been diagnosed in patients in their 20s. The average age at diagnosis is 62 for women and 69 for men. The disease is rare among both women and men.

An inverted nipple (occasionally invaginated 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. Women and men can have inverted nipples.

The specific causes of DCIS are still unknown. The risk factors for developing this condition are similar to those for invasive breast cancer.

Some women are however more prone than others to developing DCIS. Women considered at higher risks are those who have a family history of breast cancer, those who have had their periods at an early age or who have had a late menopause. Also, women who have never had children or had them late in life are also more likely to get this condition.

Long-term use of estrogen-progestin hormone replacement therapy (HRT) for more than five years after menopause, genetic mutations (BRCA1 or BRCA2 genes), atypical hyperplasia, as well as radiation exposure or exposure to certain chemicals may also contribute in the development of the condition. Nonetheless, the risk of developing noninvasive cancer increases with age and it is higher in women older than 45 years.