It's very common to have a ring of slightly darker skin around the middle of the penis. It's also normal to have a spot here or there, like a birthmark, of a lighter or darker skin color. Neither of these has anything to do with masturbation, and there's not much you can do to change it. (For more, read JackinQ&A – Questions About the Penis.)
Do you find yourself masturbating more often during some seasons than others? Why?
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