chin is lighter than rest of face, (hypopigmentation)

[shaybutterz]

I am 29 year old, black female ..  and I was wondering if anyone else has this symptom.. my skin on my face is a deep brown, however my chin looks similar however its a little bit lighter than the rest of my face, this is a lot more noticeable in the summer when I am in the sun quite a bit and my skin started to get darker.. it will get darker everywhere except my chin.. its super light and very embarrassing .. i have no idea what is causing it. I'm assuming hormonal or some kind of endocrine disorder? my doctor has not paid it any attention but it's a big concern to me. Has anyone else seen this or experienced this? i have dark patches and lines around my chin.. (hyperpigmentation) but the whole chin itself is so much lighter and will not tan or get darker for anything... it's almost as if the melanin just is not active there at all! Does anyone know what this could be related to? hormones.. and if so why? endocrine disorders? thyroid?? etc.. I'm lost.. and worried... and just plain old embarrassed by my skin... please help!