Do you have a circular mark on your arm? This reveals a historical detail that few people know.

Many older people have a small, round, sunken scar on their left arm, which often goes unnoticed or is mistaken for a common birthmark. However, this birthmark has a long history and immense medical and social significance, representing one of the most important milestones in the global fight against disease.

This distinctive scar originated from the smallpox vaccine, one of the most widespread and effective vaccination campaigns in history. For several decades in the 20th century, millions of people worldwide were vaccinated to eradicate this infectious disease, which had caused countless deaths over the centuries. The vaccine, administered en masse in many countries until the late 1970s, left an indelible mark thanks to its method of administration.

Unlike modern vaccines, which are typically administered with a single-needle syringe, the smallpox vaccine was administered using a bifurcated needle designed to make multiple punctures in the same area of ​​skin, typically 10 to 15. This procedure caused a mild reaction in the area, which typically became inflamed and crusted. After healing, the area left a circular, depressed scar that, over time, became recognizable to an entire generation.

Widespread use of this vaccine was halted between 1972 and 1980, when the World Health Organization (WHO) officially declared smallpox eradicated. With this historic decision, the virus responsible for the disease disappeared from nature. Since then, the vaccine has been administered only in very specific cases, such as to certain laboratory workers or soldiers who may have been exposed to modified versions of the virus.

One of the most frequently asked questions is whether this scar could be confused with a scar left by the BCG vaccine, used against tuberculosis. Although both vaccines leave marks on the skin, there are distinct differences: the BCG scar is typically higher and sometimes located on the right arm, while the smallpox scar is deeper, circular, and usually located on the left arm.

Beyond its historical significance, this scar may still have medical significance. Recent research suggests that people who received the smallpox vaccine as children may retain some cross-immunity to other related viruses, such as the one that causes monkeypox. While this hypothesis is still being tested, it highlights the importance of vaccination campaigns and their long-term impact.

In a certain sense, bearing this scar is like bearing witness to a pivotal moment in medical history. It’s a visible reminder of how science, through concerted effort, managed to contain and eliminate one of the most devastating diseases ever known to humanity.

So, if you notice this mark on your arm or on the arm of an elderly relative, now you know that it is not just a scar, but proof that you belong to a generation that unknowingly contributed to one of the greatest health advances of all time.