Distinct lines that form creases appear on the palms of the hands and soles of the feet. The palm has 3 of these creases in most cases. But sometimes, the creases join to form just one.

Palmar creases develop while a baby is growing in the womb, most often by the 12th week of gestation.

A single palmar crease appears in about 1 out of 30 people. Males are twice as likely as females to have this condition. Some single palmar creases may indicate problems with development and be linked with certain disorders.