Chances are you're taking in way too much sodium, or it could be the skin getting compressed because of the maxilla moving up and forwards.

Nasolabial lines are caused by differing levels of protrusion between the teeth and the rest of the maxilla. That's ignoring the obvious age factor of course.

Mew said in a video once that he'd gotten really good at being able to see the signs of maxillary upswing beginning, and then he pointed to the nasal labial area and said he sees a change there. Unfortunately he didn't name the area, nor did he describe the change he's grown accustomed to seeing during the upswing. In my experience my folds became more pronounced for a few days while an upswing took place. But there are a number of reasons these folds can become pronounced.

Pronounced as in visibility?