Post-inflammatory hyperpigmentation: This happens when the thighs darken after fungal infections like tinea cruris (AKA jock itch) or eczema heal. It may be a leftover effect or a sign of a continuing fungal infection.
Hormonal Imbalance: Changes during menstruation and pregnancy can lead to hyperpigmentation in skin folds.
Constitutional Pigmentation: Constitutional or physiological pigmentation in the inner thighs refers to the natural coloring of the skin due to genetic variations. It's quite common for the skin in the inner thigh area to be slightly darker than the surrounding skin, and this is typically a normal variation.