Most people treat them the same. They're not.
Regular dark spots sit close to the surface. Given the right ingredients and enough time, the skin sheds those pigmented cells and they fade.
Melasma forms deeper. It shows up as brownish, sometimes grayish patches on the cheeks, forehead, and upper lip — and it's driven by hormones. After 35, shifting estrogen signals the melanocytes, the cells that produce melanin, to go into overdrive. The result is melanin being produced deeper beneath the surface than any topical product is designed to reach.
That's why melasma flares around your period. Why it gets worse after even a few minutes of sun. Why starting birth control can bring it back out of nowhere. The hormones are driving it from the inside, in a layer most skincare never touches.