Brown spots on the skin are almost always caused by an overproduction of melanin, the pigment that gives skin its color. The trigger behind that overproduction varies: sun exposure, hormonal shifts, medications, and even nutritional deficiencies can all push pigment-producing cells into overdrive. Most brown spots are harmless, but knowing what’s behind yours helps you decide whether to treat them, prevent new ones, or get a closer look from a dermatologist.
How Melanin Overproduction Works
Your skin contains specialized cells called melanocytes that produce melanin. When ultraviolet light hits your skin, it damages DNA inside skin cells. That damage triggers a protein called p53, which sends a chemical signal telling melanocytes to ramp up pigment production. This is your body’s attempt at protection: melanin absorbs UV radiation and shields deeper tissue. The problem is that the protection is only moderate, and repeated UV exposure causes melanocytes in certain areas to become permanently overactive, depositing excess pigment that shows up as visible spots.
Once extra melanin is deposited, it doesn’t disappear overnight. Skin cells turn over on a cycle of roughly 40 to 56 days on average. In younger adults, the full cycle runs about 28 to 40 days. In older adults, it stretches to 60 days or more. That slower turnover is one reason brown spots become more common and more persistent with age: pigmented cells linger at the surface longer before being shed.
Sun Damage: The Most Common Cause
Solar lentigines, commonly called sunspots or age spots, are the brown spots most people are asking about. They’re flat, round, well-defined patches that range from tan to dark brown. They show up on the areas of your body that get the most sun over a lifetime: the backs of your hands, forearms, face, shoulders, and chest.
These spots are the result of years of cumulative UV exposure rather than a single bad sunburn. Each round of sun damage pushes local melanocytes to produce more pigment, and over time those cells stay “switched on” even when you’re not in the sun. That’s why sunspots tend to appear after age 40 or 50, even if you stopped tanning years ago. They’re not dangerous, but they are a visible record of UV damage to that area of skin.
Hormonal Changes and Melasma
Melasma looks different from sunspots. Instead of small, distinct dots, it produces larger, symmetrical patches that form a mask-like pattern across the face. It only appears on the face and comes in three patterns: centrofacial (across the forehead, upper lip, and chin), malar (nose and cheeks), and mandibular (along the jawline).
The trigger is hormonal. Melasma is sometimes called the mask of pregnancy because rising estrogen and progesterone levels can make pigment-producing cells hyperactive. It can also appear when you start or stop hormonal birth control, or when you begin hormone replacement therapy. Sun exposure makes it worse, but hormones are the underlying driver. Melasma often fades on its own after pregnancy or after stopping the medication that triggered it, though it can be stubborn and recur.
Post-Inflammatory Hyperpigmentation
If you’ve ever had a dark mark linger after a pimple, bug bite, cut, or rash, that’s post-inflammatory hyperpigmentation (PIH). Any injury or inflammation in the skin can cause melanocytes in the affected area to dump extra pigment as part of the healing process. The spot is flat, matches the shape of the original wound or blemish, and can range from light brown to nearly black depending on your skin tone.
PIH is especially common in people with darker skin, because their melanocytes are already more active and respond more strongly to inflammation. These marks are temporary but slow to fade, often taking months to resolve on their own. Picking at acne or scratching insect bites makes PIH worse and longer-lasting.
Medications That Cause Brown Spots
Several classes of medication can trigger skin darkening as a side effect. The patterns vary. NSAIDs like ibuprofen are often linked to fixed drug eruptions, where a round brown patch appears in the same spot each time you take the drug. The eruption itself resolves quickly, but leaves behind a lingering brown mark. Anticonvulsants such as phenytoin and carbamazepine can cause brownish-grey discoloration on the face and neck that resembles melasma, affecting roughly 10% of patients on those drugs.
Other medications associated with skin pigmentation changes include antimalarials, certain chemotherapy agents, antipsychotics, the antibiotic minocycline, and the heart medication amiodarone. Heavy metals used in older medical treatments, including gold and iron, can also cause discoloration. Iron deposits from injections can leave dark brown marks at the injection site, while gold-based treatments for joint disease have caused diffuse golden-brown pigmentation.
Vitamin B12 Deficiency
A less well-known cause of brown spots is vitamin B12 deficiency. When B12 levels drop, melanocytes become overactive, increasing both their melanin content and the activity of the enzyme that drives pigment production by as much as 131% to 135% above normal levels. B12-deficient cells also show dramatically elevated levels of reactive oxygen species (about 120% higher than normal), which further stimulates melanin production.
The dark patches from B12 deficiency tend to appear in specific locations: the backs of the hands and feet, fingers, knees, the sides of the legs, skin folds, and inside the mouth. The good news is that these pigmentation changes are reversible once B12 levels are restored through diet or supplementation.
When a Brown Spot Could Be Melanoma
The vast majority of brown spots are benign. But melanoma, the most serious form of skin cancer, can look like an unusual brown spot in its early stages. The National Cancer Institute uses the ABCDE rule to describe warning signs:
- Asymmetry: one half of the spot doesn’t match the other.
- Border irregularity: the edges are ragged, notched, or blurred, and pigment may spread into surrounding skin.
- Color variation: the spot contains uneven shades of brown, black, or tan, possibly mixed with areas of white, red, pink, 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 the past few weeks or months.
Any spot that checks one or more of these boxes warrants a professional evaluation. A spot that is changing is the single most important red flag.
Fading and Preventing Brown Spots
Topical treatments for brown spots work by slowing melanin production or speeding up cell turnover. Products containing azelaic acid (typically at 15% to 20% concentration) or hydroquinone (at 2% over the counter, 4% by prescription) are among the most studied options. Results take time. Clinical studies typically run treatment courses of four months before evaluating improvement. Other ingredients like kojic acid and vitamin C also inhibit pigment production, though they tend to work more gradually.
For deeper or more stubborn spots, clinical procedures like Q-switched laser treatments and intense pulsed light (IPL) are options. IPL can show results in fewer sessions but the improvement may be short-lived, and the skin can be quite irritated afterward. Q-switched lasers generally require more sessions but tend to keep pigmentation more controlled during recovery.
Prevention comes down to limiting UV exposure. SPF 30 sunscreen blocks 97% of UVB rays, and SPF 50 blocks 98%, so the difference between them is small. What matters more than the SPF number is consistent, generous application. Any treatment for brown spots will be undermined if you’re not protecting the area from further sun damage, because UV exposure reactivates the same melanocytes you’re trying to calm down. Wearing sunscreen daily, even on cloudy days, is the single most effective way to prevent new spots and keep treated ones from coming back.