According to the American Academy of Dermatology, the most common types of moles are skin tags, raised moles and flat moles. Benign moles are usually brown, tan, pink or black (especially on dark-colored skin). They are circular or oval and are usually small (commonly between 1–3 mm), though some can be larger than the size of a typical pencil eraser (>5 mm). Some moles produce dark, coarse hair. Common mole hair removal procedures include plucking, cosmetic waxing, electrolysis, threading and cauterization.

Some sources equate the term mole with "melanocytic nevus". Other sources reserve the term "mole" for other purposes such as the animal of the same name.

Melanocytic nevi represent a family of lesions. The most common variants are:

- Location:

- Junctional nevus: the nevus cells are located along the junction of the epidermis and the underlying dermis. A junctional nevus is flat and brown to black.

- Compound nevus: a mixture of junctional and intradermal proliferation. Compound nevi are slightly raised and brown to black. Beauty marks are usually compound nevi of either the acquired variety or congenital variety.

- Intradermal nevus: the nevus cells are located in the dermis only. Intradermal nevi are raised; most are flesh-colored (not pigmented).

- Dysplastic nevus (nevus of Clark): usually a compound nevus with cellular and architectural dysplasia. Like typical moles, dysplastic nevi can be flat or raised. While they vary in size, dysplastic nevi are typically larger than normal moles and tend to have irregular borders and irregular coloration. Hence, they resemble melanoma, appear worrisome, and are often removed to clarify the diagnosis. Dysplastic nevi are markers of risk when they are numerous (atypical mole syndrome). According to the National Cancer Institute (NIH), doctors believe that, when part of a series or syndrome of multiple moles, dysplastic nevi are more likely than ordinary moles to develop into the most virulent type of skin cancer called melanoma.

- Blue nevus: It is blue in color as its melanocytes are very deep in the skin. The nevus cells are spindle shaped and scattered in deep layers of the dermis. The covering epidermis is normal.

- Spitz nevus: a distinct variant of intradermal nevus, usually in a child. They are raised and reddish (non-pigmented). A pigmented variant, called the 'nevus of Reed', typically appears on the leg of young women.

- Acquired nevus: Any melanocytic nevus that is not a congenital nevus or not present at birth or near birth. This includes junctional, compound and intradermal nevus.

- Congenital nevus: Small to large nevus present at or near time of birth. Small ones have low potential for forming melanomas, however the risk increases with size, as in the giant pigmented nevus.

- Giant pigmented nevus: these large, pigmented, often hairy congenital nevi. They are important because melanoma may occasionally (10 to 15%) appear in them.

- Intramucosal nevus: junctional nevus of the mucosa of the mouth or genital areas. In the mouth, they are found most frequently on the hard palate.

- Nevus of Ito and nevus of Ota: congenital, flat brownish lesions on the face or shoulder.

- Mongolian spot: congenital large, deep, bluish discoloration which generally disappears by puberty. It is named for its association with East Asian ethnic groups but is not limited to them.

- Recurrent nevus: Any incompletely removed nevus with residual melanocytes left in the surgical wound. It creates a dilemma for the patient and physician, as these scars cannot be distinguished from a melanoma.

Additional types of nevi do not involve disorders of pigmentation or melanocytes. These additional nevi represent hamartomatous proliferations of the epithelium, connective tissue, and vascular malformations.

Hypermelanotic nevi must be differentiated from other types of pigmented skin lesions, including:

- Lentigo simplex

- Solar lentigo

- Café au lait macule

- Ink-spot lentigo

- Mucosal melanotic macule

- Mongolian spot (dermal melanocytosis)

A "hemangioma of infancy", colloquially called a strawberry mark, is a benign self-involuting tumor (swelling or growth) of endothelial cells, the cells that line blood vessels. It usually appears during the first weeks of life and resolves by age 10. It is the most common tumor of infancy.

PHACES Syndrome, a rare condition that often involves brain, heart, and arterial abnormalities, is generally accompanied by the presence of large facial hemangiomas. In such cases, what appears to be a small bruise or birthmark may grow rapidly and take on a puffy appearance in the first days or weeks of life.

Colloquially called a "stork bite", "angel's kiss" or "salmon patch", telangiectatic nevus appears as a pink or tanned, flat, irregularly shaped mark on the knee, back of the neck, and/or the forehead, eyelids and, sometimes, the top lip. The skin is not thickened and feels no different from anywhere else on the body; the only difference is in appearance. Nearly half of all babies have such a birthmark.

Warty dyskeratoma, also known as an Isolated dyskeratosis follicularis, is a benign epidermal proliferation with distinctive histologic findings that may mimic invasive squamous cell carcinoma and commonly manifests as an umbilicated (Having a central mark or depression resembling a navel) lesion with a keratotic plug, WD have some histopathologic similarities to viral warts but it's not caused by HPV and the majority of these lesions display overall histopathologic features consistent with a follicular adnexal neoplasm. usually limited to the head, neck, scalp or face and vulva. Lesions are generally and sporadic and may be associated with a follicular unit. Oral involvement, particularly the hard palate, and genital involvement have been reported. it can also be thought of as one of the manifestations of focal acantholytic dyskeratosis, an epidermal reaction pattern that can be seen in several disorders, including Darier's disease and Grover's disease. But the main Difference between Darier disease and Warty dyskeratoma, is that Darier disease inherited dermatosis (autosomal dominant) consisting of multiple keratotic papules on the face, trunk, and extremities, while WD occurs as an isolated, noninherited, single keratotic nodule mainly confined to the head and neck as mentioned earlier.

Warty dyskeratoma must be differentiated from vulvar dysplasia, Bowenoid papulosis, squamous carcinoma, condyloma, and other viral-induced squamous lesions.

Mongolian spots (congenital dermal melanocytosis) are birthmarks that are present at birth and most commonly located in the sacrococcygeal or lumbar area. Lesions may be single or multiple and usually involve <5% total body surface area. They are macular and round, oval or irregular in shape. The color varies from blue to greenish, gray, black or a combinations of any of the above. The size varies from few to more than 20 centimeters. Pigmentation is most intense at the age of one year and gradually fades thereafter. It is rarely seen after the age of 6 years. Mongolian spots are considered a congenital anomaly because of the various causal mechanisms scientists believe they are linked to. Melanin production, metabolism problems, or family history of Mongolian spots are some of the various causes of Mongolian spots.

A range of types of wart have been identified, varying in shape and site affected, as well as the type of human papillomavirus involved. These include:

- Common wart ("Verruca vulgaris"), a raised wart with roughened surface, most common on hands, but can grow anywhere on the body. Sometimes known as a Palmer wart or Junior wart.

- Flat wart ("Verruca plana"), a small, smooth flattened wart, flesh-coloured, which can occur in large numbers; most common on the face, neck, hands, wrists and knees.

- Filiform or digitate wart, a thread- or finger-like wart, most common on the face, especially near the eyelids and lips.

- Genital wart (venereal wart, "Condyloma acuminatum", "Verruca acuminata"), a wart that occurs on the genitalia.

- Mosaic wart, a group of tightly clustered plantar-type warts, commonly on the hands or soles of the feet.

- Periungual wart, a cauliflower-like cluster of warts that occurs around the nails.

- Plantar wart (verruca, "Verruca plantaris"), a hard sometimes painful lump, often with multiple black specks in the center; usually only found on pressure points on the soles of the feet.

Phakomatoses are inconsistently defined, and there is a lack of consensus about what conditions are included in this category.

Conditions included are:

- Ataxia telangiectasia

- Incontinentia pigmenti

- Neurofibromatosis

- Nevoid basal cell carcinoma syndrome

- Sturge-Weber syndrome

- Tuberous sclerosis

- Wyburn-Mason syndrome (Bonnet–Dechaume–Blanc syndrome)

- von Hippel-Lindau disease

Phakomatoses refers to a group of neuro-oculo-cutaneous syndromes or neurocutaneous disorders involving structures arising from the embryonic ectoderm. These multisystem disorders involve the ectodermal structures like central nervous system, skin and eyes. The lesions have a variable severity. However, it has been subsequently noted that mesodermal and endodermal tissues too are involved.

A number of genetic and acquired diseases come in this category and may affect one or more of these tissues. However, in some conditions, such as von Hippel-Lindau disease, ectodermal presentation is minimal.

Common warts have a characteristic appearance under the microscope. They have thickening of the stratum corneum (hyperkeratosis), thickening of the stratum spinosum (acanthosis), thickening of the stratum granulosum, rete ridge elongation, and large blood vessels at the dermoepidermal junction.

Carbon stains are a skin condition characterized by a discoloration of the skin from embedded carbon, usually occurring in children from accidents with firearms or firecrackers, or from a puncture wound by a pencil, which may leave a permanent black mark of embedded graphite, easily mistaken for metastatic melanoma.

Fiddler’s neck usually involves highly localized lichenification, mild hyperpigmentation, and erythema where the chin rest or instrument body presses against the skin of the neck. Other signs and symptoms include scale buildup, cyst and scar formation, papules and pustules related to local infection, and focal edema. In Blum & Ritter’s study in West Germany (1990), they found that 27% of their population had only minor issues, 72% had a palpable mass at the site, and 23% reported pain and other signs of inflammation such as hyperthermia, pulsation, and cystic, pustular, or papular lesions. Size of masses were an average of 2 cm in diameter ranging up to 4 cm, some being associated with purulent drainage, continuous discharge, and crusting. Dystrophic calcinosis cutis has also been reported. Other serious sequelae include sialolithiasis of the submandibular gland and adenolymphoma of the parotid gland.

The histopathology of fiddler’s neck frequently shows hyperkeratosis and acanthosis, along with plugging of follicles. Histiocytic infiltration with granulomas to foreign body and follicular cysts are also common. Foreign body granulomas are thought to derive from abrasion of the wooden surface of the chin rest and its absorption into the superficial dermis. The location and complex mechanism of causation for fiddler’s neck give rise to a wider spectrum of skin changes when compared to contact dermatitis from more common irritants. Fiddler’s neck can be differentiated from rosacea and sarcoid reaction with granulomas.

Symptoms include:

1. yellow-brown, banana-shaped fibers

2. caviar-like papules

3. brown-grey or blue-black hyper-pigmentation

The majority of the lesions will be seen on areas of the body that get the most sun.

Mongolian spots, or Dermal melanocytosis, result from failure of complete melanocyte migration into the epidermis before birth with ensuing dermal nesting and melanin production. If there are many spots, or a spot covers a large area, it may be a sign of an underlying disorder, such as a metabolism problem called GM1 gangliosidosis Type 1. Recent data suggest that Mongolian spots may be associated with inborn errors of metabolism. Inborn errors of metabolism arise from single gene defect, most often involving an enzyme function, which leads to disruption of a specific metabolic pathway giving rise to abnormalities in the synthesis or catabolism or proteins, fats or carbohydrates. The most common condition associated with Mongolian spots is Hurler's disease followed by GM1 gangliosidosis Type 1. The clinical manifestations in Mongolian spots in inborn errors of metabolism are spots deeper in color and have a generalized distribution involving dorsal and ventral trunk in addition to sacral region and extremities. They are persistent and in some cases an indistinct feathery border has been described. Another possible cause is through genetic inheritance. Mongolian spots have been diagnosed on several occasions through family history, Mongolian spots were linked with an autosomal dominant inheritance. The majority of the neonatal cutaneous lesions are physiological and transient requiring no therapy. It is necessary to differentiate between benign and clinically significant skin lesions in newborn. Therefore, it is important to be aware of the innocent transient skin lesions in newborn and differentiate these from other serious conditions, which will help avoid unnecessary therapy to the neonates. Parents can be assured of good prognosis of these skin manifestations.

The differential diagnoses of fiddler’s neck include branchial cleft cyst, disease of the salivary glands, tumors of the parotid gland, psoriasis, lichen planus, contact dermatitis, herpes simplex and similar infections, and insect bites and stings especially from fleas.

A supernumerary nipple (also known as a third nipple, triple nipple, accessory nipple, polythelia or the related condition: polymastia) is an additional nipple occurring in mammals, including humans. Often mistaken for moles, supernumerary nipples are diagnosed in humans at a rate of approximately 1 in 18 people.

The nipples appear along the two vertical "milk lines," which start in the armpit on each side, run down through the typical nipples and end at the groin. They are classified into eight levels of completeness from a simple patch of hair to a milk-bearing breast in miniature.

"Polythelia" refers to the presence of an additional nipple alone while "polymastia" denotes the much rarer presence of additional mammary glands.

Although usually presenting on the milk line, pseudomamma can appear as far away as the foot.

A possible relationship with mitral valve prolapse has been proposed.

It begins as painless reddish-brown nodules which slowly enlarge to form irregularly shaped red plaque.

Lupus vulgaris (also known as Tuberculosis luposa) are painful cutaneous tuberculosis skin lesions with nodular appearance, most often on the face around the nose, eyelids, lips, cheeks, ears and neck. It is the most common "M. tuberculosis" skin infection. The lesions may ultimately develop into disfiguring skin ulcers if left untreated.

The sarcoma first appears as a bruise mark, a purplish discoloration or a tender skin nodule in the extremity, typically on the anterior surface. It progresses to an ulcer with crusting, and finally to an extensive necrosis involving the skin and subcutaneous tissue. It metastasizes quickly.

Diagnosis of PG becomes clear when skin lesions progress to tense blisters during the second or third trimester. The face and mucous membranes are usually spared. PG typically starts as a blistering rash in the navel area and then spreads over the entire body. It is sometimes accompanied by raised, hot, painful welts called plaques. After one to two weeks, large, tense blisters typically develop on the red plaques, containing clear or blood-stained fluid. PG creates a histamine response that causes extreme relentless itching (pruritus). PG is characterized by flaring and remission during the gestational and sometimes "post partum" period. Usually after delivery, lesions will heal within months, but may reoccur during menstruation.

Hydroquinone-induced exogenous ochronosis is an avoidable dermatosis that is exceedingly difficult to treat.

However, some studies show that treatment may be possible with a Q-switched alexandrite (755 nm) laser.

It is recommended that individuals with this disorder stop using hydroquinone-containing compounds. It is important to be aware of this as dermatologists may think the symptoms a patient is exhibiting are a melasma, and prescribe a hydroquinone-containing cream.

Lymphangiosarcoma is a rare malignant tumor which occurs in long-standing cases of primary or secondary lymphedema. It involves either the upper or lower lymphedematous extremities but is most common in upper extremities. Although its name implies lymphatic origin, it is believed to arise from endothelial cells and may be more accurately referred to as angiosarcoma.