Ultraviolet light from the sun causes premature aging of the skin and skin damage that can lead to melanoma. Some scientists hypothesize that overexposure to UV, including excessive sunlight, may play a role in the formation of acquired moles. However, more research is needed to determine the complex interaction between genetic makeup and overall exposure to ultraviolet light. Some strong indications that this is so (but falling short of proof), are:

- The relative lack of moles on the buttocks of people with dysplastic nevi.

- Freckles (spots of melanin on the skin, and distinct from moles) are known to be influenced by sunlight.

Studies have found that sunburns and too much time in the sun can increase the risk factors for melanoma. This is "in addition to" those who have dysplastic nevi being at higher risk of this cancer (the uncertainty is in regard to acquiring "benign" moles). To prevent and reduce the risk of melanoma caused by UV radiation, the American Academy of Dermatology and the National Cancer Institute recommends staying out of the sun between 10 a.m. and 4 p.m. standard time (or whenever one's shadow is shorter than one's height). The National Cancer Institute also recommends wearing long sleeves and trousers, hats with a wide brim, sunscreens, and sunglasses that have UV-deflecting lenses.

Studies have recorded an incidence of about 3–5 cases per 1,000 newborn babies.

Usually observed at birth or shortly thereafter in 94% of patients, in other reports, patients did not develop skin lesions until 3 months or even 2 years after birth. Females are typically affected more often than males (64%).

Large and especially giant congenital nevi are at higher risk for malignancy degeneration into melanoma. Because of the premalignant potential, it is an acceptable clinical practice to remove congenital nevi electively in all patients and relieve the nevocytic overload.

Experts, such as the American Academy of Dermatology, say that vast majority of moles are benign. Nonetheless, the U.S. National Cancer Institute estimated that 62,480 new cases of melanoma and 8,420 related deaths would appear in the United States in the year 2008.

Data on the chances of transformation from melanocytic nevi to melanoma is controversial, but it appears that about 10% of malignant melanomas have a precursor lesion, of which about 10% are melanocytic nevi. Therefore, it appears that malignant melanoma quite seldomly (1% of cases) has a melanocytic nevi as a precursor.

The decision to observe or treat a nevus may depend on a number of factors, including cosmetic concerns, irritative symptoms (e.g., pruritus), ulceration, infection, and concern for potential malignancy.

The prognosis is favorable in most patients with an isolated cutaneous abnormality. In the majority of cases, both the vivid red marking and the difference in circumference of the extremities regress spontaneously during the first year of life. It is theorized that this may be due to the normal maturation process, with thickening of the epidermis and dermis. Improvements for some patients can continue for up to 10 years, while in other cases, the marbled skin may persist for the patient's lifetime.

One study reported an improvement in lesions in 46% of patients within 3 years. If CMTC persists into adulthood, it can result in complaints due to paresthesia, increased sensitivity to cold and pain, and the formation of ulcers.

Few reports included long-term follow up of CMTC into adolescence and adulthood. While about 50% of patients seem to show definite improvement in the reticular vascular pattern, the exact incidence and cause of persistent cases are unknown.

Halo nevi are estimated to be present in approximately 1% of the general population, and are found to be more prevalent in people with vitiligo, malignant melanoma, or Turner syndrome. All races and sexes are equally susceptible to this disease, although a familial tendency has been reported. The average age of onset is in a person's teenage years.

These nevi represent excess growth of blood vessels, including capillaries.

- Nevus simplex (also known as a stork bite, salmon patch, or Nevus flammeus neonatorum)

Port-wine stains were shown to be caused by a somatic activating c.548G→A mutation in the GNAQ gene. An association with RASA1 has also been described.

Large congenital nevi are caused by a mutation in the body's cells that occurs early in embryonic development, usually within the first twelve weeks of pregnancy. Mutations are sometimes found in genes that code for NRAS and KRAS proteins. There is no known method of prevention.

Spitz nevi are uncommon. Their annual incidence was estimated in a coastal population of sub-tropical Queensland to be 1.4 cases per 100,000 people. For comparison, the annual incidence of melanoma in the same population, which is high by world standards is 25.4 cases per 100,000 people.

Although they are most commonly found on people in their first two decades of life, the age range for people with Spitz nevi is from 6 months to 71 years, with a mean age of 22 years and a median age of 19 years.

As halo nevi are only of cosmetic significance, no treatment is required, and patients will be asymptomatic. Although halo nevi are harmless, it is important to monitor the lesion on regular basis. Watch out for any changes in appearance of existing or new halo nevi. If there is any change in appearance or is associated with pain, itch, and infection, a doctor should be consulted immediately to exclude the possibility of melanoma.

Phakomatosis pigmentovascularis is a rare neurocutanous condition where there is coexistence of a capillary malformation (port-wine stain) with various melanocytic lesions, including dermal melanocytosis (Mongolian spots), nevus spilus, and nevus of Ota.

Nevus sebaceus or sebaceous nevus (the first term is its Latin name, the second term is its name in English; also known as an "organoid nevus" and "nevus sebaceus of Jadassohn") is a congenital, hairless plaque that typically occurs on the face or scalp. Such nevi are present at birth, or early childhood, affecting males and females of all races equally. The condition is named for an overgrowth of sebaceous glands in the area of the nevus.

Skin growths such as benign tumors and basal cell carcinoma can arise in sebaceous nevi, usually in adulthood. Rarely, sebaceous nevi can give rise to sebaceous carcinoma. However, the rate of such malignancies is now known to be less than had been estimated. For this reason, excision is no longer automatically recommended.

Nevoid melanoma is a cutaneous condition that may resemble a Spitz nevus or an acquired or congenital melanocytic nevus.

Pseudomelanoma (also known as a "recurrent melanocytic nevus", and "recurrent nevus") is a cutaneous condition in which melantic skin lesions clinically resemble a superficial spreading melanoma at the site of a recent shave removal of a melanocytic nevus.

Blue nevus (also known as "blue neuronevus", "dermal melanocytoma", and "nevus bleu") is a type of melanocytic nevus. The blue colour is caused by the pigment being deeper in the skin than in ordinary nevi. In principle they are harmless but they can sometimes be mimicked by malignant lesions, i.e. some melanomas can look like a blue nevus.

The melanocytes left behind in the wound regrow in an abnormal pattern. Rather than the even and regular lace like network, the pigments tends to grow in streaks of varying width within the scar. This is often accompanied by scarring, inflammation, and blood vessel changes – giving both the clinical and histologic impression of a melanoma or a severe dysplastic nevus. When the patient is reexamined years later without the assistance of the original biopsy report, the physician will often require the removal of the scar with the recurrent nevus to assure that a melanoma is not missed.

Mucinous nevus (also known as "Nevus mucinosus") is a rare cutaneous condition characterized by hamartoma that can be congenital or acquired.

Phakomatosis pigmentokeratotica is a rare neurocutanous condition characterized by the combination of an organoid sebaceous nevus and speckled lentiginous nevus. It is an unusual variant of epidermal naevus syndrome. It was first described by Happle "et al". It is often associated with neurological or skeletal anomalies such as hemiatrophy, dysaesthesia and hyperhidrosis in a segmental pattern, mild mental retardation, seizures, deafness, ptosis and strabismus.

Nevus of Ota (also known as "congenital melanosis bulbi", "nevus fuscoceruleus ophthalmomaxillaris", "oculodermal melanocytosis", and "oculomucodermal melanocytosis") is a blue hyperpigmentation that occurs on the face. It was first reported by Dr. M.T. Ota of Japan in 1939.

Nevus of Ota is caused by the entrapment of melanocytes in the upper third of the dermis. It is found on the face unilaterally and involves the first two branches of the trigeminal nerve. The sclera is involved in two-thirds of cases (causing an increased risk of glaucoma). It should not be confused with Mongolian spot, which is a birthmark caused by entrapment of melanocytes in the dermis but is located in the lumbosacral region. Women are nearly five times more likely to be affected than men, and it is rare among Caucasian people. Nevus of Ota may not be congenital, and may appear during puberty.

Phakomatosis pigmentovascularis is subdivided into five types:

- Type 1 PWS + epidermal nevus

- Type 2 (most common): PWS + dermal melanocytosis +/- nevus anemicus

- Type 3: PWS + nevus spilus +/- nevus anemicus

- Type 4: PWS + nevus spilus + dermal melanocytosis +/- nevus anemicus

- Type 5: CMTC (Cutis marmorata telangiectatica congenita) + dermal melanocytosis

They all can contain capillary malformation. Type 2 is the most common and can be associated with granular cell tumor. Some further subdivide each type into categories A & B; with A representing oculocutaneous involvement and subtype B representing extra oculocutaneous involvement. Others have proposed fewer subtypes but currently this rare entity is mostly taught as having five subtypes currently.

There is no treatment, but because this is a benign condition with no serious clinical complications, prognosis is excellent.

A Spitz nevus (also known as an epithelioid and spindle-cell nevus, benign juvenile melanoma, and "Spitz's juvenile melanoma") is a benign melanocytic nevus, a type of skin lesion, affecting the epidermis and dermis.

The name "juvenile melanoma" is generally no longer used as it is misleading: it is not a melanoma, it is a benign lesion; and it can also occur in adults, not only in children.