The thing is, there really isn’t a clear definition—it’s more of a colloquial distinction, and there are some conflicting opinions. “Fine lines are often mistaken for baby lines,” says board-certified dermatologist Joshua Zeichner, MD, because the faint spots can eventually turn into deeper lines. “Others consider them to be separate entities unrelated to facial expression, but more a function of UV light,” he adds, because UV light changes the underlying elastic structure of the skin, which can cause small, tissue-like folds ( also known as crepe skin).

But again, there is no hard and fast rule to separate the two in dermatology. “If you have five dermatologists in a room, you’re probably going to get five different opinions on what a wrinkle is, not a line,” adds Zeichner. Of course, you can always assess the crease itself: a fine line often appears, well, thin and faint, while a wrinkle can be more static and deep. But even that can be subjective, depending on what you consider “good”.