Milk blister without lactating?

So...on my right nipple I have what really truly looks like every picture I've ever seen of a milk blister. But here's the thing: I'm not lactating. Unless it's somehow possible to lactate just enough to develop a blister but not enough to create noticeable moisture.

Anybody know anything about what could be going on? The bump appeared sometime in the last year or so but doesn't hurt or seem to be getting bigger or smaller. For what it's worth, I've never been pregnant and have a copper IUD.