Last year I got a moderately-deep cut on my finger, and it left a scar. Six months later, the scar is still there. On the other hand, I've had lots of other cuts on my fingers, though none have left scars. Why is this? Is scarring related to the severity of the cut, or something else?
This depends on a number of factors. Here are the first two that come to mind:
1) Is the cut deep enough to reach the dermis (this is the layer below the epidermis) where scar tissue will form?
2) What is your general state of health, and was there an infection at the site of the cut, which would have altered the normal healing process.
Basically, not all cuts are created equal, especially if some are deeper than others and become infected.
This article studied scratch depth http://www.ncbi.nlm.nih.gov/pubmed/17440346