Sun exposure, friction from clothing or shaving, post-acne marks, and dead skin cell buildup are the most common causes, often building up gradually over months or years.

Kojic acid, which works by slowing the skin's excess melanin production, gradually reducing the appearance of dark spots rather than masking them.

Yes. Dark underarms are usually caused by the same friction and pigment-production process as dark spots elsewhere, so kojic acid can be applied there the same way as on any other part of the body.

Typically 3-6 weeks with consistent daily use, since pigment-focused ingredients work gradually by affecting new pigment production, not by immediately erasing existing spots.

Both. Gentle regular exfoliation helps clear the dead skin cells sitting on top of pigmented areas, which supports and speeds up how visible the brightening process is.