The small round mark that many people have on the upper arm is the scar left by the BCG vaccine, given mainly at birth to protect against the most severe forms of tuberculosis.
After receiving the vaccine, a small bump usually appears that over time can turn into a blister or superficial wound. As it heals, it leaves a permanent scar, which is a normal sign that the body reacted to the vaccine and developed defenses against the disease.
Although not everyone keeps a visible mark, it is very common in countries where BCG is part of the childhood vaccination schedule.
