I ditto the comment that a dull blade may have helped cause this. It has been suggested that a mushroom brush is good for cleaning this out. Also - it appears that your mat is older and dried out a bit. Olfa suggests that you periodically soak your cutting mats in warm water and let them dry flat - this helps keep the mat moist. I do mine in the bathtub where they can lay almost totally flat. Do not put in direct sun to dry since that might cause warping.