Scar tissue is dead tissue.
Tissue dies when there is no blood flow to the area.
Tissue also dies when it has been inflamed for too long.
PREVENT scar tissue with the following:
1. small gauge needles.
2. slow injection speed.
3. frequent massage.
4. rotating inject sites.
IMO, the above represents the most influential factors of scar tissue in
order of importance.
There's no real SET time limit for scar tissue to 'develop' and depending
on how you do things mentioned above you could get a lot in a short
time or get none ever.
Take care and you can avoid completely. Just like you can avoid serious
sides of gear with regular bloodwork and constant monitoring.