It is a familiar and demoralising pattern. Months of steady progress through winter and spring. Then summer arrives, and by September the patches are back roughly where they started — despite doing everything correctly.
The usual explanation is that you weren't strict enough. Often that isn't it.
Sunscreen is tested against something narrower than you think
The SPF number on a bottle describes protection against UVB, the wavelengths that cause burning. Broad-spectrum labelling adds UVA, which penetrates more deeply and contributes to both ageing and pigmentation.
Neither measure says anything about visible light — the part of the spectrum you can actually see. And visible light, especially the high-energy blue-violet portion, is a genuine driver of pigmentation. The research on this has firmed up considerably over the past decade, and the effect is strongest in exactly the skin tones where melasma is most common.
So a conventional sunscreen, applied perfectly, still leaves a meaningful trigger completely unaddressed. In summer, when both the intensity and the number of hours outdoors go up, that gap widens.
Four things stacking up at once
Visible light exposure rises sharply
Longer days, more time outside, more reflected light off water, sand, and pavement. Reflected light matters more than people assume — sand and water bounce a substantial fraction of what hits them straight back up at your face, from below, where shade and hat brims don't help.
Heat itself is a factor
Raised skin temperature appears to stimulate melanogenesis independently of light exposure. It is a smaller effect than UV, but it runs in the same direction, and it explains why some people see flare-ups from hot environments — cooking, saunas, hot climates — with no strong sun exposure.
Reapplication almost never happens properly
Sunscreen is tested at 2 mg per square centimetre. Most people apply somewhere between a quarter and half of that, and reapply far less often than the two-hourly guidance. Real-world protection is routinely a fraction of the number on the bottle.
Summer routines get harsher
More exfoliation, more actives, more "clearing" products, often alongside more sun. Irritation is itself a pigmentation trigger — post-inflammatory hyperpigmentation stacks on top of whatever you were already dealing with.
What actually helps
Switch to a tinted sunscreen
This is the single highest-leverage change, and it is not cosmetic. The iron oxides that create the tint physically block visible light in a way that transparent mineral and chemical filters do not. Trials comparing tinted against untinted formulations in melasma have consistently favoured the tinted versions.
Look for iron oxides on the ingredients list. "Tinted" without them may just be colourant.
Apply substantially more than feels natural
Roughly a third of a teaspoon for the face alone. Most people's instinctive amount is well under half of that. If a bottle is lasting you months of daily use, you are almost certainly underapplying.
Reapply on a timer, not on instinct
Every two hours outdoors. Powder and stick formats exist specifically because reapplying a cream over makeup is impractical — using a less elegant format that you actually reapply beats a better one that you don't.
Treat window light as real exposure
Standard glass blocks most UVB but transmits UVA and essentially all visible light. Car side windows, office windows, and home windows all count. If you sit next to a window for hours daily, that is meaningful cumulative exposure.
Ease off the actives in peak season
Counterintuitive, but sound. Aggressive exfoliation and high-strength actives during your highest-exposure months often costs more in irritation-driven pigmentation than it gains. Many dermatologists deliberately run gentler summer routines and push the heavier work to autumn and winter.
Reframing the year
The most useful mental shift is to stop treating this as a continuous improvement project and start treating it as seasonal.
Autumn and winter are when ground gets gained — lower exposure, more room for actives, better tolerance. Spring and summer are for holding position: protection-first, gentler routine, realistic goals.
Judged that way, a summer where things stayed roughly level is a good summer, not a failure. The people who get frustrated and escalate their routine in July are usually the ones who end September worse off.
The short version: your sunscreen is probably fine against UV and doing nothing against visible light. Switch to a tinted formula with iron oxides, apply about three times what feels natural, and treat summer as a holding season rather than a progress season.