Dark spots on the skin form when clusters of cells produce more melanin, the pigment that gives skin its color, than the surrounding area. The result is a flat or slightly raised patch that’s darker than your natural skin tone. The triggers range from sun exposure and hormonal shifts to inflammation, medications, and underlying health conditions.
How Dark Spots Form
Your skin contains specialized cells called melanocytes that produce melanin through a chain of chemical reactions. The process starts when an enzyme converts the amino acid tyrosine into a pigment precursor, which then gets packaged into tiny compartments and distributed to nearby skin cells. This is what gives your skin its baseline color and helps protect it from UV damage.
Dark spots appear when something disrupts this system. A variety of signals, from UV radiation to hormones to inflammatory chemicals, can push melanocytes to ramp up pigment production or cause melanin to accumulate unevenly. The specific trigger determines what kind of dark spot you get, where it shows up, and how long it lasts.
Sun Damage: The Most Common Cause
Chronic UV exposure is responsible for the flat brown spots that many people call “age spots” or “liver spots.” The clinical name is solar lentigines, and they typically appear on the face, hands, shoulders, and forearms after years of cumulative sun exposure. UV radiation causes mutations in skin cells that enhance melanin production and trap melanin in the outer layer of skin. Interestingly, the number of melanocytes in these spots is usually normal or only slightly increased. It’s the activity level, not the cell count, that drives the darkening.
Tanning beds accelerate this process because they deliver stronger UV rays than natural sunlight. Certain medical light therapies can also trigger these spots as a side effect. Solar lentigines tend to be permanent without treatment because the underlying mutations don’t reverse on their own.
Hormonal Shifts and Melasma
Melasma produces larger, blotchy brown or gray-brown patches, most often on the cheeks, forehead, nose, and upper lip. It develops when melanocytes go into overdrive in response to hormonal changes, and it affects women far more often than men.
Pregnancy is one of the most common triggers. The rise in estrogen and progesterone during pregnancy stimulates melanocytes, which is why melasma has long been called “the mask of pregnancy.” Birth control pills can have the same effect by altering hormone levels. Thyroid problems also increase melasma risk because an improperly functioning thyroid gland disrupts the hormonal balance your skin cells respond to.
Stress may play a role as well. When the body produces more cortisol under chronic stress, that hormonal surge can trigger melanocytes to produce excess pigment. Sunlight makes melasma worse regardless of the original cause, since UV exposure compounds the hormonal signal by independently stimulating more melanin production. This is why melasma patches often darken in summer and lighten somewhat in winter.
Dark Marks After Skin Injuries
If you’ve ever noticed a brown or purple-brown mark lingering long after a pimple healed, that’s post-inflammatory hyperpigmentation (PIH). It happens after any kind of skin injury or irritation: acne, eczema flare-ups, burns, cuts, insect bites, or even aggressive skin treatments like chemical peels or laser procedures.
When skin is injured, the inflammatory response releases chemical signals, including prostaglandins and other compounds produced from the breakdown of fatty acids in cell membranes. These signals stimulate nearby cells to release factors that tell melanocytes to produce more pigment. The process is essentially a communication chain: damaged skin cells send distress signals to support cells, which then relay “make more melanin” messages to melanocytes. The result is a dark patch that outlasts the original wound by weeks or months.
PIH is more common and more visible in people with darker skin tones, because their melanocytes are already producing more pigment and respond more intensely to inflammatory triggers. These marks are not scars. They sit in the upper layers of skin and typically fade on their own, though it can take anywhere from a few months to over a year without treatment.
Medications That Darken Skin
A surprisingly long list of medications can cause dark spots as a side effect. The discoloration can appear as scattered spots, patches in sun-exposed areas, or even a diffuse blue-gray tint affecting the nails and skin.
Some of the more commonly implicated drug categories include:
- Antibiotics: Certain types, particularly minocycline (used for acne and infections), can cause blue-gray patches on the skin, especially in areas exposed to sunlight.
- Antimalarials: Drugs like quinacrine have been linked to diffuse blue-gray pigmentation on the nail beds and face after long-term use.
- Cancer chemotherapy agents: Many chemotherapy drugs cause hyperpigmentation as a known side effect.
- Psychiatric medications: Long-term use of tricyclic antidepressants and some tranquilizers has been associated with slate-gray discoloration in sun-exposed skin.
- Hormonal medications: Beyond birth control pills triggering melasma, other hormone therapies can cause uneven pigmentation.
- Heart and blood pressure medications: Some of these make the skin more sensitive to sunlight, indirectly promoting dark spots.
If you notice new dark spots after starting a medication, bring it up with your prescriber. The pigmentation sometimes fades after the medication is stopped, but not always.
Nutritional Deficiencies
Vitamin B12 deficiency can cause a distinctive pattern of hyperpigmentation. The darkening tends to show up on the backs of the hands and feet, in skin folds, and sometimes on the nails, tongue, or inside the mouth. Specific signs include dark spots on the lips, dark streaks running lengthwise along the fingernails, and hyperpigmented patches on the palms. These changes typically improve once B12 levels are restored, though it can take time.
Insulin Resistance and Dark Patches
Dark, velvety patches in the folds of the neck, armpits, or groin are a hallmark of a condition called acanthosis nigricans. Unlike most other dark spots, these patches have a distinct texture: they feel thicker and softer than the surrounding skin, almost like velvet.
The mechanism is directly tied to insulin levels. When the body becomes resistant to insulin, it compensates by producing more. At high concentrations, insulin crosses into the outer layer of skin and binds to growth receptors on skin cells, stimulating them to multiply rapidly. This overgrowth of skin cells is what creates the thickened, darkened patches. Acanthosis nigricans is one of the earliest visible signs of insulin resistance and type 2 diabetes, so it’s worth getting your blood sugar checked if you notice these patches developing.
Seborrheic Keratoses: Spots That Aren’t Flat
Not every dark spot is a pigmentation issue. Seborrheic keratoses are extremely common growths that appear as waxy, slightly raised bumps ranging from light tan to dark brown or black. They have a characteristic “pasted on” look, as if someone dripped candle wax onto the skin, and their surface often feels rough or scaly. They typically show up on the face, chest, shoulders, and back.
These are completely benign and unrelated to sun damage, hormones, or inflammation. They’re primarily a product of aging and genetics. The main reason to know about them is to avoid confusing them with other types of dark spots. If a spot is raised, waxy, and looks like it could be peeled off, it’s likely a seborrheic keratosis rather than a sun spot or melanoma.
Treatment Options
Treatment depends on what’s causing the dark spots and how deep the pigment sits in your skin. For sun-related spots and melasma, topical products that slow down the enzyme responsible for melanin production are the first-line approach. These are often combined with antioxidants and anti-inflammatory ingredients to address multiple steps in the pigmentation process at once. Newer delivery systems using nanoparticles and liposomes help these active ingredients penetrate the skin more effectively than older formulations.
For spots that don’t respond to topical treatment, procedures like fractional lasers, intense pulsed light, and microneedling can target melanin deposits without causing significant damage to the surrounding skin. These approaches carry a small risk of triggering new pigmentation, especially in darker skin tones, so finding an experienced provider matters.
Sun protection is the single most important step regardless of the cause. UV exposure worsens virtually every type of dark spot and can undo the results of treatment. Daily broad-spectrum sunscreen, protective clothing, and shade during peak hours aren’t just prevention strategies; they’re an essential part of any treatment plan for existing spots.