What Causes Dark Patches On Thigh And Arms?

hello doctor,
am having dark patches on my upper thigh on my right leg..its been for 8years now..its slowly growing..now its appearing on my arms too...i had a biopsy,they saying they are not viral or any kind of fungus...it might go off naturally..its still there its started increasing on my arms too...i'm very worried..plz help me with a answer...