First thing, Indian skin behaves differently.

We have more melanin. Good thing overall, but it also means our skin reacts faster to sun, acne and irritation by producing extra pigment.

Common triggers:

Sun exposure (biggest culprit, always)

Acne marks (post-inflammatory hyperpigmentation)

Hormonal changes (melasma) »

Heat + friction (even from masks or dupattas sometimes)

And once these spots settle in, they take their own time leaving.