The mechanical properties of skin are important factors in everything from forensic science to razor blade design. And yet studies that have actually measured these properties are few and far between, most research in this area being done on synthetic or animal skin.

Today, Aisling Nı Annaidh at University College Dublin in Ireland and a few pals right this wrong with a detailed analysis of the mechanical properties of 56 pieces of skin removed from dead humans. In the process, these guys have settled a debate about the nature of skin strength that has puzzled anatomists since the 19th century.

The first detailed study of skin strength was carried out in the 1860s by Karl Langer, an Austrian anatomist working in Vienna. He mapped the natural lines of tension within skin by puncturing the skin on a cadaver with a circular tool and then measuring the shape of the resulting hole.

The tension within the skin makes these holes elliptical in a direction parallel to the tension. Consequently, a simple measurement of the orientation of these ellipses allowed Langer to map out lines of force in the skin over the entire body. Today, these lines are known as Langer lines.