The Truth Behind the Mysterious Round Scar on the Upper Arm
Many people notice a small, round scar on their upper arm and wonder where it came from. The truth is simple: in most cases, this mark is not from an injury—it’s from a childhood vaccine.
What Causes This Scar?
The most common cause is the BCG vaccine (Bacillus Calmette–Guérin), which is used to protect against tuberculosis (TB). This vaccine is usually given during infancy in many countries around the world.
Why Does It Leave a Mark?
Unlike most vaccines, the BCG vaccine is injected just under the skin. After the injection:
A small bump appears
It may turn into a tiny sore
As it heals, it leaves a permanent round scar
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