I had a diabetic friend who was very worried about skin tracks. She had to inject herself regularly and no matter how carefully she did it, she began to accumulate marks on her regular injection sites.
And the doctors were worried she would damage the skin or the veins there, so she had to keep swapping to new places. It's hard enough having to inject yourself at all, without doing it in a different place each time.
I felt so bad for her. Luckily they are starting to come up with methods of injection that are so non-invasive that they don't leave marks, almost like hypo-sprays in sci-fi movies.
I just hope they get them out to the general market before my friend winds up with real medical problems from her tracks.