Skin discoloration happens when your body produces too much or too little melanin, the pigment that gives skin its color. The causes range from sun exposure and hormonal shifts to inflammation, infections, medications, and underlying medical conditions. Understanding the specific trigger matters because treatments vary widely depending on what’s driving the pigment change.
How Melanin Production Goes Wrong
Melanin is manufactured by specialized cells called melanocytes, which sit in the deepest layer of your skin. The process depends on an enzyme called tyrosinase, which converts the amino acid tyrosine into melanin through a series of chemical steps. Tyrosinase is the bottleneck of the entire system. Anything that revs it up causes darkening, and anything that shuts it down or destroys melanocytes causes lightening.
When melanocytes become overactive, they pump extra pigment into surrounding skin cells, creating dark patches or spots. When they’re destroyed or disabled, the affected skin loses its color entirely. Vitiligo, for example, results from the immune system attacking and killing melanocytes, leaving stark white patches with no pigment at all.
Sun Damage and Sunspots
Chronic UV exposure is the most common cause of permanent dark spots. UV radiation triggers melanocytes to ramp up pigment production as a protective response, but over time this process becomes dysregulated. The cells that receive the excess melanin (called keratinocytes) begin to show signs of cellular aging: they grow larger, accumulate DNA damage, and release inflammatory signals that perpetuate the cycle.
These spots, called solar lentigines, typically first appear in your 30s, usually around the temples and cheeks. After age 40 or 50, they tend to multiply, darken, and spread to larger areas. They’re most common on skin that gets repeated sun exposure: the face, hands, forearms, and chest. Unlike a tan, which fades when UV exposure stops, solar lentigines are essentially permanent changes in how that patch of skin produces pigment.
Hormonal Changes and Melasma
Hormones are powerful drivers of skin pigmentation. Estrogen and progesterone both directly increase the activity of tyrosinase and related enzymes, which is why melasma (symmetrical brown or gray-brown patches, usually on the face) so commonly appears during pregnancy or while taking hormonal birth control. An estimated 50% to 70% of pregnant women in the U.S. develop melasma, with rates reaching up to 80% among pregnant Latina women. About one-third of those affected continue to have melasma for the rest of their lives.
Estrogen works through multiple routes. It binds to receptors inside melanocytes and directly turns up the genes responsible for melanin-producing enzymes. It also activates receptors on the cell surface that trigger rapid signaling cascades, amplifying pigment output even further. Progesterone adds to the problem by promoting blood vessel growth and inflammatory signals in the skin, which in turn stimulate melanocyte activity. This is why melasma can be so stubborn: multiple hormonal pathways are feeding into it simultaneously.
Melasma isn’t exclusively a women’s issue. In clinical samples, about 10% of white melasma patients and 26% of Indian melasma patients are men. People with medium to dark skin tones are at highest risk because their melanocytes are already more active at baseline.
Post-Inflammatory Hyperpigmentation
Any injury or inflammation in the skin can leave behind dark marks. Acne, eczema, burns, cuts, bug bites, and even aggressive skincare treatments can trigger this response. During inflammation, your skin releases a cocktail of chemical messengers, including prostaglandins, interleukins, tumor necrosis factor, and reactive oxygen species. These signals stimulate nearby melanocytes to produce extra pigment, which then gets deposited in the healing skin.
The resulting dark patches can last weeks, months, or even years. Post-inflammatory hyperpigmentation is especially common and visible in people with darker skin tones, and it’s one of the most frequent reasons people with brown or black skin seek dermatologic care. The discoloration itself isn’t scarring, though it often accompanies scars from acne or injury. It typically fades on its own, but the timeline can be frustratingly slow without treatment.
Fungal Infections
Tinea versicolor is a common fungal skin infection that creates patches of lighter (or sometimes darker) skin, usually on the chest, back, and upper arms. It’s caused by Malassezia, a yeast that naturally lives on everyone’s skin but can overgrow in warm, humid conditions. The fungus produces azelaic acid, a compound that inhibits or damages melanocytes in the affected area, bleaching the skin underneath. This is why the light patches often become most noticeable after sun exposure: the surrounding skin tans normally, but the affected patches can’t produce pigment.
Medications That Change Skin Color
Dozens of medications can alter skin pigmentation, and the color of the change often hints at the mechanism. Brown discoloration usually means the drug is stimulating your melanocytes to overproduce melanin. Gray, blue, or violet discoloration typically means the drug itself, or one of its byproducts, is physically depositing in the skin.
Some of the most commonly implicated drug categories include:
- Chemotherapy drugs like bleomycin, cisplatin, and doxorubicin
- Antimalarials like hydroxychloroquine
- Certain antibiotics, particularly minocycline (which can cause blue-gray patches)
- Heart medications like amiodarone
- Anti-seizure drugs like phenytoin
- Oral contraceptives
- Some antidepressants and antipsychotics
Heavy metals like silver, iron, and bismuth can also deposit in skin and cause discoloration. In many cases, the pigment change fades after stopping the medication, though some drugs leave permanent marks.
Adrenal Insufficiency and Other Systemic Conditions
Generalized skin darkening, especially in skin creases, gums, and areas that get friction, can signal an internal medical problem. The classic example is Addison’s disease, where the adrenal glands stop producing enough cortisol. When cortisol drops, the brain’s feedback system kicks into overdrive and floods the body with a precursor hormone that gets cleaved into both a stress hormone and melanocyte-stimulating hormone. The result is a bronze-like darkening across the body, often most prominent on the knuckles, elbows, and inside the mouth.
Other systemic conditions that can cause widespread pigment changes include thyroid disorders, liver disease, and hemochromatosis (iron overload), which gives skin a characteristic bronze or slate-gray tone.
Vitamin Deficiencies
Vitamin B12 deficiency can cause hyperpigmentation, particularly on the knuckles, nail beds, and skin folds. The mechanism involves increased activity of tyrosinase, the same enzyme central to normal melanin production. In B12-deficient patients, the skin cells that normally receive melanin from melanocytes become abnormally large (a hallmark of B12 deficiency throughout the body), and this disrupts the normal transfer process. The net effect is darker patches in characteristic locations. Correcting the deficiency with B12 supplementation typically reverses the discoloration over several months.
How Dermatologists Identify the Cause
When the cause isn’t obvious from your history, dermatologists use a tool called a Wood’s lamp, which emits ultraviolet light in the 320 to 450 nanometer range. Under this light, pigment changes that sit in the upper skin layers (epidermal) become more pronounced, while deeper pigment changes (dermal) stay relatively unchanged. This distinction helps narrow down the diagnosis because different conditions deposit pigment at different skin depths. Melasma, for instance, can be epidermal, dermal, or mixed, and the type determines which treatments are most likely to work.
The pattern, location, and color of discoloration carry diagnostic clues. Symmetrical patches on the face suggest melasma or sun damage. Scattered light spots on the trunk point toward tinea versicolor. Darkening in skin folds and creases raises concern for a hormonal or systemic cause. Blue-gray patches in someone taking medication suggest drug deposition rather than melanin overproduction.