Why a baby was born with a tail: the scientific explanation

A case involving a newborn with an extremely rare anomaly has been reported in Brazil: a "true human tail" measuring approximately 12 centimeters in length, featuring a spherical mass 4 centimeters in size. Typically, an embryonic tail forms between the fourth and eighth weeks of pregnancy but subsequently regresses and is reabsorbed during development. In this specific case, however, the infant was born prematurely at 35 weeks, and doctors noticed the protrusion after birth. Following specialist examinations—and having ruled out immediate risks, given that it was an isolated cutaneous finding—the decision was made to surgically remove the tail and the associated mass.