It can be due to oral melanotic macule, fixed drug eruption or simple hyperpigmentation. Hyperpigmentation occurs when an excess of melanin, the brown pigment that produces normal skin color, forms deposits in the skin.
Treatment involves hydroquinone, azelaic acid, corticosteroids, tretinoin cream and laser treatment. Please discuss these options with your dermatologist before using them.
Hope it helps. Take care and please do keep me posted on how you are doing or if you have any additional queries. Warm regards.
Thanks for the response. So this probably happened just from being outside, nothing that I did? Also, will it eventually come back on its own or to have it come back I would need to talk to a dermatologist?