Melanin is the natural pigment that gives skin, hair, and eyes their color. Cells called melanocytes make it, and they live in the bottom layer of the epidermis. Melanin also protects the skin by absorbing ultraviolet (UV) light from the sun.
Melanin is a normal part of the skin, not a diagnosis. IPathology reports often mention it in relation to moles, melanoma, and other pigmented spots. This article explains how melanin is made, what it looks like under the microscope, and why it appears in your report.
How is melanin made and used?
Melanocytes make melanin and pack it into tiny granules. They pass these granules through long, branching arms to the nearby keratinocytes, the main cells of the epidermis. Inside the keratinocytes, the melanin forms a small cap over the nucleus. This cap shields the cell’s genetic material from UV damage.
The number of melanocytes is similar in people of all skin colors. Differences in skin color come from how much melanin those melanocytes make and what type it is. Sun exposure increases melanin production, which is why skin tans.
What does melanin look like under the microscope?
Under the microscope, melanin appears as fine brown-to-black granules. It is found inside melanocytes, inside keratinocytes, and sometimes inside macrophages in the dermis. Macrophages that have swallowed melanin are called melanophages.
Melanin can look similar to hemosiderin, a brown pigment left behind by old bleeding. To tell them apart, the pathologist may use an iron stain. The iron stain turns hemosiderin blue but does not change melanin. Another special stain, called the Fontana-Masson stain, turns melanin black.
Why is melanin mentioned in a pathology report?
Pathology reports mention melanin for several reasons:
- Moles and melanoma. Most moles and many melanomas contain melanin. The report may describe how much pigment is present and where it is found.
- Other pigmented growths. Some growths that are not made of melanocytes still contain melanin. For example, a pigmented basal cell carcinoma contains melanin that the tumor collects from nearby melanocytes.
- Flat brown spots. Some spots are brown because the skin makes extra melanin without an increase in melanocytes. An oral melanotic macule is one example.
- Melanophages in the dermis. After inflammation or injury, melanin can drop into the dermis and be taken up by macrophages. This can leave a brown or gray mark on the skin. Melanophages are also seen in some moles and melanomas that have partly regressed.
Does every melanoma contain melanin?
No. Some melanomas make little or no melanin. They are called amelanotic melanomas, and they can look pink or skin-colored rather than brown. For this reason, pathologists do not rely on pigment to identify melanocytes.
Instead, pathologists can use immunohistochemistry to detect proteins made by melanocytes. Common markers include SOX10, Melan-A, and HMB-45. These markers can identify melanocytes whether or not they contain melanin.
Heavy melanin can make these stains harder to read, because the stains usually show up as a brown color. Some laboratories use a red color instead or chemically remove the melanin, so the result is easier to see.
Questions to ask your doctor
- Why does my report mention melanin?
- Is the melanin in melanocytes, skin cells, or macrophages?
- Does the pigment explain the color of my skin spot?
- Was a special stain used to identify the pigment?
- What is the final diagnosis in my report?
- Do I need any further treatment or follow-up?
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