Key points
- Melanoma begins in melanocytes, the cells that make skin pigment.
- It is different from cancers that begin in other kinds of skin cells.
- A mole is not the same thing as melanoma; melanoma can also begin on skin without a mole.
- Risk factors describe increased chances across groups, and cancer statistics cannot predict an individual outcome.
This page is general information, not medical advice. Your own doctor or care team is the right source for questions about your skin, diagnosis or treatment.
Melanoma is a cancer of pigment-making cells. Understanding those cells, the skin around them, and the words used to describe the disease can make other information easier to follow. The same word may appear in a report, a letter, or a general article, but those documents answer different questions. A general explanation gives the meaning of a term; your care team can explain what it means in your own situation.
Pigment cells and the skin around them
The National Cancer Institute's skin cancer prevention summary explains that melanocytes lie in the lower part of the epidermis, the outer skin layer. They produce melanin, the pigment responsible for the skin's natural color. When skin is exposed to sunlight, these cells can make more pigment, causing the skin to darken.
Beneath the epidermis is the dermis, which contains blood vessels, glands, and hair follicles. The fat-containing tissue underneath is called the subcutaneous layer. The National Cancer Institute's SEER melanoma reference shows these layers and places melanocytes near the bottom of the epidermis. The diagram here shows this arrangement in a simple outline; it does not show a particular person's skin or a diagnosis.
The layers have different jobs and different kinds of cells. The National Cancer Institute distinguishes basal cell carcinoma, which begins in basal cells, and squamous cell carcinoma, which begins in squamous cells, from melanoma, which begins in melanocytes. Basal and squamous cell cancers are often grouped under the name nonmelanoma skin cancer. A report naming one of those cancers is describing a different disease from melanoma.
The explanation of how skin works looks more closely at the layers, pigment cells, and the tissue that gives skin its structure. These are features of the normal organ that help explain the language used when its cells change.
Where melanoma can begin
The National Cancer Institute's reference on moles and melanoma describes melanoma as a cancer that can enter nearby tissue and spread elsewhere in the body. Most melanocytes are in the skin, so much of the public information about melanoma concerns skin melanoma. It can begin on any skin surface, including areas that do not receive much sunlight.
The same reference explains that melanoma can begin in the eye, under a nail, in the digestive tract, and in other areas. Melanoma of the eye is called uveal melanoma. Mucosal melanoma refers to melanoma in the moist linings of certain body passages. These names identify where the disease began. The types of melanoma page explains these site names and the main skin subtypes.
Moles, atypical moles, and melanoma
A common mole is a cluster of melanocytes. Its medical name is nevus; the plural is nevi. The National Cancer Institute describes common moles as usually round or oval, with an even color and a clear edge. Common moles are not cancer. A dysplastic nevus, sometimes called an atypical mole, looks different from an ordinary mole in features such as its border, color, or surface.
The institute makes an important distinction: an atypical mole is a risk factor for melanoma, but it is not itself a diagnosis of melanoma. Either an ordinary or an atypical mole can become melanoma, but this happens rarely. More often, melanoma develops on an area of skin that previously looked normal. Information about melanoma therefore concerns new skin changes as well as changes in existing moles.
The skin self-exam and warning signs page explains how agencies describe noticing changes. Appearance alone cannot establish the diagnosis. The National Cancer Institute says that diagnosis requires removing tissue and examining it for cancer cells. The skin biopsy explanation describes what a tissue sample is and how it is examined.
What a risk factor means
A risk factor is something associated with a greater chance of developing a disease. It is not a prediction that a person will develop it. The National Cancer Institute lists melanoma risk factors that include skin that burns easily, many moles, unusual moles, a personal or family history of melanoma, and a weakened immune system.
Its references also describe sunlight, artificial ultraviolet radiation from tanning devices, and a history of blistering sunburns as risk factors. Ultraviolet radiation is invisible energy that can damage skin. Some risk factors concern past exposure, while others concern inherited traits or medical history. They cannot be reduced to a judgment based only on the color of someone's skin or on a single mole.
The institute notes that people with any skin color can develop skin cancer. Differences in average risk do not identify what an individual spot is. Likewise, a risk-factor list is not a test that can rule melanoma in or out. A doctor's assessment addresses a person's skin and history rather than simply counting items on that list.
A personal history means that someone has had melanoma before. A family history concerns melanoma or unusual moles in relatives. The National Cancer Institute describes both as relevant to risk. It also notes that sunburns during adulthood, as well as earlier in life, are associated with increased melanoma risk. These histories describe different kinds of information rather than a single cause that explains every case.
How common melanoma is
The National Cancer Institute's SEER Cancer Stat Facts estimate 112,000 new cases of melanoma of the skin in the United States in 2026, representing 5.3% of all new cancer cases. These are estimates about a population. They concern melanoma of the skin and should not be read as counts of all eye or mucosal melanomas.
The National Cancer Institute's explanation of cancer statistics says that data from large groups cannot predict exactly what will happen to one person. Survival statistics also concern people diagnosed years earlier, and may not reflect treatments in use now. No personal outcome follows from a population number. Questions about an individual diagnosis belong with the doctor or care team who knows that person's circumstances.