- Individuals are differentiated in decades of life by different shading colours from: white: 1st decade of life; light grey: 2nd decade of life; medium grey: 3rd decade of life; grey: 4th decade of life; dark grey: 5th decade of life. M male, F female, PNS Peripheral Nervous System, GERD Gastroesophageal reflux disease (– no, + mild, + + moderate, + + + severe), SGD Sweat Gland Density: gland number/cm2