Ask most people what causes dark spots and you'll get one answer: sun. It's not wrong. It's incomplete, and that's usually why the routine stalls: sunscreen goes on, a brightening serum gets added, and eight months later the same spot is still there. Excess pigment comes from a handful of different signals: UV exposure, hormones, inflammation, a compromised barrier. All of them converge on the same outcome, melanocytes producing more melanin than they should. Most products are built to interrupt one of those signals. Most complexions are dealing with more than one.
The shared endpoint
Every one of these triggers ends at the same place. A melanocyte gets a signal, ramps up an enzyme called tyrosinase, and starts overproducing melanin. We broke that part down in detail in our piece on tranexamic acid: how the signaling cascade works, and how it can be interrupted at the ingredient level. This post is about what flips the switch in the first place: four separate links in the same chain, each one capable of triggering pigment entirely on its own.
Cause 1: UV exposure — not just damage, a signal
Sun exposure does more than create pigment directly. It triggers a cascade. UV radiation causes DNA stress in skin cells, which sets off the release of a hormone called alpha-MSH. That hormone binds to a receptor on melanocytes, activating the enzyme tyrosinase and telling it to start producing melanin. Melanin is your skin's built-in UV filter, so the response is protective by design. It just doesn't switch off cleanly, and it compounds with every unprotected exposure. That's why "just wear sunscreen" is correct and still not the whole answer: sunscreen blocks this input. It doesn't touch the other three links in the chain.
Cause 2: Hormones — melasma's real driver
Melasma shows up in symmetrical patches, often across the cheeks and upper lip, and doesn't respond well to standard brightening. That's because it isn't triggered by UV or injury. It's driven by estrogen and progesterone acting directly on melanocytes, stimulating the same tyrosinase pathway from a hormonal angle instead of a UV one. It's why melasma shows up during pregnancy, with hormonal birth control, and during other hormonal shifts. It's also why melasma is notoriously hard to manage with sun protection alone. You can't SPF your way out of a hormonal trigger. It's a different link, with its own switch.
Cause 3: Inflammation — the mark a breakout leaves behind
Post-inflammatory hyperpigmentation is what's left after a breakout, an irritation, or an injury heals. Inflammation releases compounds such as prostaglandins, cytokines, and related signaling molecules that stimulate melanocytes to produce more melanin and hand it off to surrounding skin cells. That's why a healed blemish can leave a mark that outlasts the blemish itself by months. It also means anything that irritates the complexion, including pore-clogging ingredients hiding in your products, over-exfoliation, harsh actives, or aggressive extractions, can plant the next round of pigment even when the sun never touches it. Sunscreen and hormone management don't do anything about an active inflammatory response. That link needs its own answer too.
Cause 4: A compromised barrier — the one nobody blames
This is the trigger that gets missed most often. A damaged barrier puts skin into a state of low-grade, ongoing inflammation. Not a breakout. Just a constant low hum of irritation. That chronic inflammation sends the same signal described above: melanocytes told to stay switched on. No single flare. No obvious trigger. Just a complexion that holds onto pigment and won't let it fade, because the underlying inflammation never fully resolves. An over-stripped, over-exfoliated, or chronically irritated complexion holds onto pigment longer than one with an intact barrier. You can address the other three causes perfectly and still lose ground here if the barrier itself never gets resolved.
Why these rarely show up alone
These four causes compound. This is the pattern that shows up over and over in the treatment room. Someone comes in having already tried two or three different brightening products, frustrated that none of them worked. The answer usually isn't that the products failed. It's that each one only ever addressed one cause. Hormonal melasma gets worse with UV exposure. Post-inflammatory marks linger longer on a complexion whose barrier is already compromised. Someone dealing with stubborn, treatment-resistant pigment is usually managing two or three of these triggers at once. Not one. That's the actual reason a lot of "brightening" products underdeliver: they're aimed at a single cause on a complexion running multiple triggers at once.
What this means for how you treat hyperpigmentation
The real fix isn't a better single ingredient. It's addressing all four causes, because whichever one gets left out keeps producing pigment no matter what you're doing about the rest. Sunscreen addresses cause one. It does nothing for hormones, inflammation, or barrier status. A tyrosinase inhibitor can suppress production once a signal's already firing, but it doesn't touch a hormonal trigger, calm active inflammation, or repair a compromised barrier. None of these four causes substitutes for another. Treat only one and the other three keep running, whether or not you notice them yet.
Causes one through three funnel into the same downstream pathway: a signal that activates tyrosinase, and tyrosinase that produces melanin. That's the pathway P.C. Serum interrupts. Tranexamic acid, azelaic acid, and THD Ascorbate work on the signal and production steps regardless of whether UV, hormones, or inflammation triggered them. Cause four doesn't run through that pathway the same way. It's an ongoing state, not a single trigger, and a pigment serum doesn't resolve it. That's what G.C. Cleanser and F.S.N. Hydrator are for: a barrier-safe cleanse that doesn't add to the problem, and a barrier-support formula that calms the inflammation keeping cause four active. Skip either one, and the barrier keeps feeding pigment production the serum alone can't offset. Treat the causes, not just the output — all four, not whichever one your current routine happens to cover.
