A healthcare provider can usually diagnose a port-wine stain based entirely upon the history and appearance. In unusual cases, a skin biopsy may be needed to confirm the diagnosis. Depending on the location of the birthmark and other associated symptoms, a physician may choose to order a measurement of intraocular pressure or X-ray of the skull.

A MRI scan of the brain may be performed (under anesthesia) on infants who have a port-wine stain in the head area in order to check for signs of Sturge-Weber syndrome.

If the port-wine stain is inside the mouth, a provider may check the insides of a newborn baby's throat with a scope to see if there are any changes (growths) other than just the color.

If the port-wine stain is around the eye or on the eyelid, a referral may be made to an optometrist or ophthalmologist for a test of the ocular pressures in that eye. If swelling occurs in the port-wine stain, it may cause vision problems, glaucoma, or blindness.

In the absence of successful treatment, hypertrophy (increased tissue mass) of the stains may cause problems later in life, such as loss of function (especially if the stain is near the eye or mouth), bleeding, and increasing disfigurement. Lesions on or near the eyelid can be associated with glaucoma. If the port-wine stain is on the face or other highly visible part of the body, its presence can also cause emotional and social problems for the affected person.

It is suggested that gene therapy might be used as a cure in the future.

Clinical diagnosis can be made with the naked eye using the ABCD guideline or by using dermatoscopy. An online-screening test is also available to help screen out benign moles.

The management of a nevus depends on the specific diagnosis, however, the options for treatment generally include the following modalities:

Nevi are typically diagnosed clinically with the naked eye or using dermatoscopy. More advanced imaging tests are available for distinguishing melanocytic nevi from melanoma, including computerized dermoscopy and image analysis. The management of nevi depends on the type of nevus and the degree of diagnostic uncertainty. Some nevi are known to be benign, and may simply be monitored over time. Others may warrant more thorough examination and biopsy for histopathological examination (looking at a sample of skin under a microscope to detect unique cellular features). For example, a clinician may want to determine whether a pigmented nevus is a type of melanocytic nevus, dysplastic nevus, or melanoma as some of these skin lesions pose a risk for malignancy. The ABCDE criteria (asymmetry, border irregularity, color variegation, diameter > 6 mm, and evolution) are often used to distinguish nevi from melanomas in adults, while modified criteria (amelanosis, bleeding or bumps, uniform color, small diameter or de novo, and evolution) can be used when evaluating suspicious lesions in children. In addition to histopathological examination, some lesions may also warrant additional tests to aid in diagnosis, including special stains, immunohistochemistry, and electron microscopy. Typically; the nevi which exist since childhood are harmless

Some patients have a few or no histopathologic abnormalities. Histological examination of a biopsy may show an increase in the number and size of capillaries and veins (rarely lymphatics), dilated capillaries located in the deeper dermis, and hyperplasia and swollen endothelial cells with occasional dilated veins and venous lakes.

It often requires a dermatologist to fully evaluate moles. For instance, a small blue or bluish-black spot, often called a blue nevus, is usually benign but often mistaken for melanoma. Conversely, a junctional nevus, which develops at the junction of the dermis and epidermis, is potentially cancerous.

A basic reference chart used for consumers to spot suspicious moles is found in the mnemonic A-B-C-D, used by institutions such as the American Academy of Dermatology and the National Cancer Institute. The letters stand for asymmetry, border, color, and diameter. Sometimes, the letter E (for elevation or evolving) is added. According to the American Academy of Dermatology, if a mole starts changing in size, color, shape or, especially, if the border of a mole develops ragged edges or becomes larger than a pencil eraser, it would be an appropriate time to consult with a physician. Other warning signs include a mole, even if smaller than a pencil eraser, that is different from the others and begins to crust over, bleed, itch, or become inflamed. The changes may indicate developing melanomas. The matter can become clinically complicated because mole removal depends on which types of cancer, if any, come into suspicion.

A recent and novel method of melanoma detection is the "ugly duckling sign" It is simple, easy to teach, and highly effective in detecting melanoma. Simply, correlation of common characteristics of a person's skin lesion is made. Lesions which greatly deviate from the common characteristics are labeled as an "ugly duckling", and further professional exam is required. The "little red riding hood sign", suggests that individuals with fair skin and light colored hair might have difficult-to-diagnose melanomas. Extra care and caution should be rendered when examining such individuals as they might have multiple melanomas and severely dysplastic nevi. A dermatoscope must be used to detect "ugly ducklings", as many melanomas in these individuals resemble non-melanomas or are considered to be "wolves in sheep clothing". These fair skinned individuals often have lightly pigmented or amelanotic melanomas which will not present easy-to-observe color changes and variation in colors. The borders of these amelanotic melanomas are often indistinct, making visual identification without a dermatoscope very difficult.

People with a personal or family history of skin cancer or of dysplastic nevus syndrome (multiple atypical moles) should see a dermatologist at least once a year to be sure they are not developing melanoma.

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.

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%).

Since the histopathology of nevus anemicus is normal, nevus anemicus is a pharmacologic nevus and not an anatomic one. In most people a nevus anemicus is on a covered area and so light in appearance that no treatment is needed.

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

In general, children with a small isolated nevus and a normal physical exam do not need further testing; treatment may include potential surgical removal of the nevus. If syndrome issues are suspected, neurological, ocular, and skeletal exams are important. Laboratory investigations may include serum and urine calcium and phosphate, and possibly liver and renal function tests. The choice of imaging studies depends on the suspected abnormalities and might include skeletal survey, CT scan of the head, MRI, and/or EEG.

Depending on the systems involved, an individual with Schimmelpenning syndrome may need to see an interdisciplinary team of specialists: dermatologist, neurologist, ophthalmologist, orthopedic surgeon, oral surgeon, plastic surgeon, psychologist.

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.

A Q-switched laser has been successfully used to treat the condition.

Most birthmarks are harmless and do not require treatment. Pigmented marks can resolve on their own over time in some cases. Vascular birthmarks may require reduction or removal for cosmetic reasons. Treatments include administering oral or injected steroids, dermatological lasers to reduce size and/or color, or dermatologic surgery.

Benign congenital nevi can have histological characteristics resembling melanomas, often breaking most if not all of the ABCDE rules. Dermatoscopic findings of the smaller forms of benign congenital nevi can aid in their differentiation from other pigmented neoplasms.

Microscopically, congenital melanocytic nevi appear similar to acquired nevi with two notable exceptions. For the congenital nevus, the neval cells are found deeper into the dermis. Also, the deeper nevus cells can be found along with neurovascular bundles, with both surrounding hair follicles, sebaceous glands, and subcutaneous fat. Such annexes and the hypodermis can also be hypoplasic or, conversely, present aspects of hamartoma.

These are localized white spots on skin which may affect any area of the body, but these white spots are quite stable lesions. In the majority of patients, the lesions are not completely achromic, but are hypopigmented and resemble splashed paint. The individual lesions are permanent and there are no effective therapies for re-pigmenting this nevus. If there is hair in an affected area, it is usually colourless or white.

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.

Spider angiomas are asymptomatic and usually resolve spontaneously. This is common in the case of children, although they may take several years to disappear. If the spider angiomas are associated with pregnancy, they may resolve after childbirth. In women taking oral contraceptives, they may resolve after stopping these contraceptives. The spider angiomas associated with liver disease may resolve when liver function increases or when a liver transplant is performed.

For spider angiomas on the face, techniques such as electrodesiccation and laser treatment can be used to remove the lesion. There is a small risk of a scar, although the results are generally good. Spider angiomas can recur after treatment.

Different therapeutic modalities have been attempted to repigment the lesions of nevus depigmentosus such as PUVA, excimer laser, and different grafting techniques. PUVA therapy has not been shown to be beneficial. Successful repigmentation was reported in a single case with 14 sessions of excimer laser treatment. Though the repigmentation of nevus depigmentosus is possible by grafting techniques, the results are inconsistent and recurrence is possible. In consideration of the experience of other authors and us, the quality and retention of pigment are unpredictable. These factors need to be considered while consulting and offering any treatment to the patient of nevus depigmentosus.

As Becker's nevus is considered a benign lesion, treatment is generally not necessary except for cosmetic purposes. Shaving or trimming can be effective in removing unwanted hair, while electrology or laser hair removal may offer a longer-lasting solution. Different types of laser treatments may also be effective in elimination or reduction of hyperpigmentation, though the results of laser treatments for both hair and pigment reduction appear to be highly variable.

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.

Also known as "scoop", "scallop", or "shave" excisional biopsy, or "shave excision". A trend has occurred in dermatology over the last 10 years with the advocacy of a deep shave excision of a pigmented lesion An author published the result of this method and advocated it as better than standard excision and less time consuming. The added economic benefit is that many surgeons bill the procedure as an excision, rather than a shave biopsy. This save the added time for hemostasis, instruments, and suture cost. The great disadvantage, seen years later is the numerous scallop scars, and a very difficult to deal with lesions called a "recurrent melanocytic nevus". What has happened is that many "shave" excisions does not adequately penetrate the dermis or subcutanous fat enough to include the entire melanocytic lesion. Residual melanocytes regrow into the scar. The combination of scarring, inflammation, blood vessels, and atypical pigmented streaks seen in these recurrent nevus gives the perfect dermatoscopic picture of a melanoma. When a second physicians re-examine the patient, he or she has no choice but to recommend the reexcision of the scar. If one does not have access to the original pathology report, it is impossible to tell a recurring nevus from a severely dysplastic nevus or a melanoma. As the procedure is widely practiced, it is not unusual to see a patient with dozens of scallop scars, with as many as 20% of the scars showing residual pigmentation. The second issue with the shave excision is fat herniation, iatrogenic anetoderma, and hypertrophic scarring. As the deep shave excision either completely remove the full thickness of the dermis or greatly diminishing the dermal thickness, subcutanous fat can herniate outward or pucker the skin out in an unattractive way. In areas prone to friction, this can result in pain, itching, or hypertrophic scarring.

A 1991 report documented the cases of nine patients with both Becker's nevus and malignant melanoma. Of the nine melanomas, five were in the same body area as the Becker's nevus, with only one occurring within the nevus itself. As this was apparently the first documented co-occurrence of the two diseases, there is so far no evidence of higher malignancy rates in Becker's nevi versus normal skin. Nonetheless, as with any abnormal skin growth, the nevus should be monitored regularly and any sudden changes in appearance brought to the attention of one's doctor.

Port-wine stains, also known as nevus flammeus and sometimes mistaken for strawberry marks, are present at birth and range from a pale pink in color, to a deep wine-red. Irregular in appearance, they are usually quite large, and caused by a deficiency or absence in the nerve supply to blood vessels. This causes vasodilation, the dilation of blood vessels, causing blood to pool or collect in the affected area. Over time, port-wine stains may become thick or develop small ridges or bumps, and do not fade with age. Such birthmarks may have emotional or social repercussions. Port-wine stains occur in 0.3% of the population, equally among males and females. They frequently express unilaterally, i.e., on only one side, not crossing the midline of the body. Often on the face, marks on the upper eyelid or forehead may be indicative of a condition called Sturge-Weber syndrome. Additionally, port-wine stains in these locations may be associated with glaucoma and seizures.