Well, there's no way of knowing for sure which one is causing it... that's the problem. :?
I'd say start off with any recently added hairs since it just occurred for you, but it's mainly through trial and error. Whenever your scalps go back to normal in that hair bin is when you know that the problem hair is out of there. You'd still have to go in your downloads folder later and find the mesh for that hair and get rid of it since it'd be useless afterwards, but as long as its recolors are out of the game, it shouldn't cause much more annoyance other than wasted space.
I'd also suggest to make note of the hair you delete during the "witch hunt" that wasn't the cause of the problem, so you can find it and re-download it if it was an innocent file.
