If you glance at the upper left arm of many adults, you might notice a small, round scar. For some, it’s barely visible; for others, it’s more pronounced, slightly indented, or darker than the surrounding skin. Most people received it as children, often without explanation, and grew up never questioning why it remained. Today, curiosity about this tiny mark is rising as people pay closer attention to their bodies and health history.
A Scar Rooted in Public Health History
The familiar mark is most often the result of the BCG vaccine, short for Bacillus Calmette–Guérin. Developed in the early 20th century, the vaccine was designed to protect against tuberculosis (TB), a potentially deadly bacterial infection that primarily affects the lungs but can also spread throughout the body.
Tuberculosis was once a leading cause of death worldwide, particularly among children. Before antibiotics became widely available, vaccination was one of the most effective ways to prevent the disease. Consequently, the BCG vaccine became a routine part of childhood immunization programs across Europe, Asia, Africa, and parts of South America.
