I have semi-dark patches on my skin. It usually is less visible right after some tough shower scrubbing but it won't fully go away. What may this be?

Dark Patches. Postinflammatory hyperpigmentation is a frequently encountered problem and represents the sequelae of various cutaneous disorders as well as therapeutic interventions. This acquired excess of pigment can be attributed to various preceding disease processes that affect the skin such as infections, allergic reactions, mechanical injuries, reactions to medications, phototoxic eruptions, trauma.