Understanding Smallpox Vaccination Marks and Their Cause

I have a clear memory of noticing a distinct scar on my mother’s arm when I was a child. It was located high on her upper arm, close to the shoulder, and had a very specific circular pattern that immediately caught my attention.

The mark looked like a cluster of small indents surrounding a slightly deeper central point, almost like a faded imprint from something long past. At the time, I could not explain why I found it so interesting, but I remember staring at it more than once during ordinary moments at home.