How is the medullary index of hair calculated?

The medullary index of hair is a measure of the width of the medulla relative to the width of the entire hair shaft. It is calculated by dividing the average medullary diameter by the average hair shaft diameter and multiplying by 100.

To measure the medullary index, a cross-section of the hair is cut and viewed under a microscope. The width of the medulla and the width of the entire hair shaft are then measured using a calibrated eyepiece or a digital image analysis system. The measurements are taken at multiple locations along the hair shaft, and the average values are used to calculate the medullary index.

The medullary index can vary depending on the type of hair, the location of the hair on the body, and the individual's age and health. In general, human scalp hair has a medullary index of around 35%, while body hair has a lower medullary index of around 20%.

The medullary index can be used to identify different types of hair, and it can also be used to assess the quality of hair. Hair with a high medullary index is often considered to be healthier and more resistant to damage than hair with a low medullary index.