Dark patches form when your skin overproduces melanin — usually triggered by sun exposure, hormones, inflammation, or genetics. Common culprits include melasma and post-inflammatory hyperpigmentation. They show up more often in darker skin tones and can linger without treatment, but they're harmless and almost always treatable.
Your skin makes melanin to protect itself from UV damage. When the sun hits, melanin production spikes — sometimes unevenly — and dark patches form. But sun exposure is only part of the picture. Hormones are a huge trigger. About 90% of melasma cases occur in women, often starting during pregnancy or when beginning hormonal birth control. A woman who never had skin discoloration in her 20s can develop butterfly-shaped patches across her cheeks within weeks of getting pregnant — that's classic melasma. Skin trauma matters too. Acne breakouts, eczema flares, or even a small cut can leave dark marks behind as the skin heals. This is called post-inflammatory hyperpigmentation, and it's especially common in Fitzpatrick skin types III–VI (medium to deep tones). Your genetics also set the baseline. People with more melanin-rich skin are simply more prone to hyperpigmentation — not because their skin is weaker, but because it's more reactive to triggers. And here's one most people miss: fragrance in your daily moisturizer can irritate skin enough to cause localized darkening over time. If you're noticing patches where product sits, that might be why.
Dark patches don't show up randomly — they tend to flare at predictable times. Summer is the biggest culprit. UV rays directly stimulate melanin production, and more time outdoors means more exposure. Even sitting near a sunny window counts: UVA rays penetrate glass easily and can quietly deepen existing patches over weeks. Hormonal shifts are another reliable trigger. Melasma often appears or worsens during pregnancy, while on the pill, or around perimenopause — times when estrogen levels fluctuate significantly. Heat itself can also trigger melasma flares in hormonally sensitive skin, independent of UV exposure. Post-acne marks tend to surface 1–2 weeks after a breakout clears, as inflammation fades and the skin overcompensates with pigment. The more you pick at spots, the darker those marks typically become. And if you've recently switched skincare products — especially anything with active exfoliants like retinol or AHAs — temporary irritation can trigger new darkening in sensitive areas before your skin adjusts.
Many people believe dark patches are permanent and impossible to fade—they're not. With consistent treatment like vitamin C serums, hydroquinone, or professional treatments like laser therapy, most patches improve significantly within 2-4 months. Another misconception: that dark patches only happen to people with darker skin. While it's true they're more visible and common in deeper skin tones, melasma affects all ethnicities, including fair-skinned individuals. People also think sunscreen alone will prevent them, but SPF without avoiding direct sun exposure during peak hours (10 AM–4 PM) won't stop stubborn melasma from returning. Lastly, many assume dark patches indicate skin cancer—they almost never do. Hyperpigmentation is purely cosmetic and benign.
Melasma in particular tends to spread if UV exposure or hormonal triggers continue unchecked. It often appears in symmetrical patterns — both cheeks, across the forehead, or along the upper lip — and once one area is affected, others can follow. Daily SPF 50+ and limiting direct sun during peak hours are your most reliable ways to stop new patches from forming.
UV rays directly stimulate melanin production, so more sun exposure equals more pigment. Warmer months usually mean longer time outdoors — but even indoor exposure matters. UVA rays pass through windows and can gradually deepen patches even if you never go outside. Heat is also an independent trigger for melasma in hormonally sensitive skin, which is why some people notice flares even when they've been careful with sunscreen.
Start with OTC ingredients — niacinamide, vitamin C, and azelaic acid are all well-evidenced and gentle enough for most skin types. Give them a real 8–12 week trial with consistent daily use before calling it. If you're not seeing meaningful improvement after that, book a dermatologist appointment. Prescription hydroquinone, retinoids, or in-office treatments like laser and chemical peels are significantly more powerful and can cut treatment time considerably.