Brown spots appear on skin when certain cells produce too much melanin, the pigment that gives skin its color. This can happen for several reasons: sun exposure, hormonal changes, inflammation from injuries or acne, and simple aging. A large international survey of 48,000 people across 34 countries found that 50% of the population reported having at least one pigmentary disorder, making brown spots one of the most common skin concerns worldwide.
How Melanin Creates Dark Spots
Your skin color comes from melanin, a pigment made by specialized cells called melanocytes. These cells contain tiny factories called melanosomes, where an enzyme called tyrosinase kicks off a chain reaction. It converts the amino acid tyrosine into a series of intermediate compounds that eventually become melanin. When this process runs normally, melanin spreads evenly through your skin. When something triggers melanocytes to become overactive, or when melanin clumps together in one area, a visible brown spot forms.
There are two types of melanin. Eumelanin produces brown and black tones, while pheomelanin produces reddish and yellowish tones. The ratio between them, along with how much total melanin your melanocytes produce, determines both your baseline skin color and what your brown spots look like. Most common brown spots involve an excess of eumelanin concentrated in a small patch of skin.
Sun Damage Is the Most Common Cause
Ultraviolet light from the sun speeds up melanin production. That’s the same process behind a tan, but when skin has endured years of UV exposure, the melanocytes in certain areas start misfiring. They produce melanin in high concentrations or allow it to clump together, creating flat brown patches known as solar lentigines, commonly called age spots or sun spots.
These spots are most common in adults over 50, but younger people can develop them too if they spend significant time in the sun. They tend to show up on areas that get the most exposure: the face, backs of the hands, forearms, and shoulders. Solar lentigines accounted for 27% of all pigmentary disorders in the international survey mentioned above, making them the single most common type of brown spot.
Hormonal Changes and Melasma
Melasma produces larger, often symmetrical patches of brown or grayish-brown discoloration, typically across the cheeks, forehead, nose, or upper lip. It’s driven by hormones rather than sun damage alone, though sun exposure makes it worse. Pregnancy is one of the most common triggers because rising levels of estrogen and progesterone stimulate melanocytes to become more active. Birth control pills can have the same effect.
Women between ages 20 and 40 are most commonly affected, and melasma is far more frequent in women than men overall. About 11% of people surveyed across 34 countries reported having it. Beyond reproductive hormones, thyroid problems and even stress may play a role. Stress raises cortisol levels, and some research suggests that elevated cortisol can trigger melasma in people who are already predisposed.
Brown Marks After Acne or Injury
If you’ve ever had a pimple, burn, cut, or rash leave behind a dark mark that lasted weeks or months, that’s post-inflammatory hyperpigmentation (PIH). It happens because inflammation in the skin activates the same melanin-producing pathways that sun exposure does. When skin is inflamed, it releases a cascade of signaling molecules that ramp up melanocyte activity and boost the enzyme tyrosinase, which drives melanin production into overdrive.
PIH is especially common in people with darker skin tones. Darker skin naturally has more active melanocytes, which makes it more prone to producing excess pigment after any kind of skin injury. The marks are flat, not raised, and can range from light brown to very dark brown depending on skin tone and how deep the pigment sits. About 15% of people in the global survey reported PIH, making it nearly as common as melasma.
These marks are not scars. They don’t involve changes in skin texture, just color. Most fade on their own over months, though deeper pigment deposits can take a year or longer to resolve without treatment.
Raised Brown Spots and Growths
Not every brown spot is flat. Two common types of raised brown lesions look quite different from each other and carry different implications.
Seborrheic keratoses are waxy, slightly raised growths that look almost “stuck on” to the skin surface. They’re oval or round, can be brown, tan, or black, and often have a scaly or wart-like texture. They tend to grow larger and thicker over time. These are benign and extremely common in middle-aged and older adults. They don’t become cancerous.
Actinic keratoses, on the other hand, are rough, scaly, dry patches caused by cumulative sun damage. They can feel gritty or sandpaper-like, and sometimes you notice the texture before you see the color change. These are considered precancerous because a small percentage can progress to skin cancer if left untreated. Some appear as horn-like growths. If you have a rough, persistent scaly patch on sun-exposed skin, it’s worth having it evaluated.
How Skin Tone Affects Brown Spots
Brown spots don’t look the same on everyone. On lighter skin, sun spots and melasma tend to appear as clearly defined tan or medium-brown patches. On darker skin, the same conditions may appear as deeper brown or grayish patches, and post-inflammatory hyperpigmentation tends to be more prominent and longer-lasting. This is because darker skin has more active melanocytes that respond more strongly to any stimulus, whether that’s UV light, hormones, or inflammation.
The visibility of brown spots also varies. On very light skin, even a small increase in melanin production creates an obvious contrast. On medium to dark skin, some spots blend more subtly with surrounding skin but may sit deeper in the skin layers, which can make them slower to fade.
When a Brown Spot Could Be Melanoma
The vast majority of brown spots are harmless. But melanoma, the most dangerous form of skin cancer, also starts as a dark spot or an existing mole that changes. The National Cancer Institute uses the ABCDE criteria to help distinguish normal spots from potentially dangerous ones:
- Asymmetry: one half of the spot doesn’t match the other half
- Border: the edges are ragged, notched, or blurred rather than smooth
- Color: the spot has uneven shading, with mixes of brown, black, tan, white, gray, red, or blue
- Diameter: the spot is larger than about 6 millimeters (roughly the size of a pencil eraser), though melanomas can be smaller
- Evolving: the spot has changed in size, shape, or color over recent weeks or months
A single feature from this list doesn’t necessarily mean cancer, but any spot that is evolving, has irregular borders, or contains multiple colors deserves a closer look from a dermatologist. This is especially true for new spots that appear after age 50 or spots that look noticeably different from all your other moles.