eraser tool "white line"

I'm using Adobe Pse 14 and I need to know if there Is there a way to use the eraser tool without it leaving  a "white line" on the edge I am erasing? when erasing I've noticed an edge remains (or is created) along the image I'm trying to erase. It is quite obvious and I can't get rid of it, especially when I'm stacking layers or if there is a dark layer beneath it. someone has to of seen this before and I want to know how to keep this from happening. It also happens with all erasers(especially the magic eraser) and all file formats jpeg's,  bmp's, png;s. Has anyone seen this and know how to eliminate it?  Thanks in advance.    C