The Minor test (starch-iodine test) described by Minor in 1928 is a qualitative test used to evaluate sudomotor function (sweating).
Method
An iodine solution is applied to the skin and allowed to air-dry. Once dry the area is dusted with cornstarch or potato flour. Sweating is then encouraged with the aid of pilocarpine, the use of a sauna or exercise.
When sweat reaches the surface of the skin the starch and iodine combine causing a dramatic color change (yellow -> dark blue) allowing sweat production to be actively visualized.
Uses
The minor test can be used as a diagnostic tool to evaluate underactive (hypohidrosis) and overactive (hyperhidrosis) sweating.