.dermatologysocal.com
"Hyper pigmentation is the over production of the natural pigment in your skin. Some of us have hyper pigmentation from an early age that may have a genetic component. For others, it is a result of hormone shifts, the use of birth control pills as in the case of melasma or a pregnancy mask during and after pregnancy.
For most of us, though, splotchy skin and brown markings on the face, chest, arms and hands are a direct result of sun exposure."
I'm not seeing any concrete explanations which is sad because this thread is so old and so many have the same issue. ^^ This is what I found that sorta makes sense for how my week has been. My body and birth control have been at odds for a couple weeks now, and the splotches showed up 3-4 days ago, across both hands but mostly on the right. I've had them before but didn't think anything of it and they went away. This time I was more curious. The only other odd thing I did this week was weeding/clearing the garden. No sun exposure though, as it's still transitioning from winter to spring here ... though I am 21, maybe my liver is overworked from the birthcontrol ups and downs along with the hormonal shifts ... I am not a doctor, but this is what I think it is for my case
http://en.wikipedia.org/wiki/Melasma