What is FSC and SSC in flow cytometry?

In flow cytometry, the light scattered by cells is measured by two optical detectors: forward scatter (FSC) that detects scatter along the path of the laser, and side scatter (SSC) which measures scatter at a ninety-degree angle relative to the laser.

FSC intensity is proportional to the diameter of the cell, and is primarily due to light diffraction around the cell. FSC signal can be used for the discrimination of cells by size. SSC, on the other hand, is from the light refracted or reflected at the interface between the laser and intracellular structures, such as granules and nucleus. SSC provides information about the internal complexity (i.e. granularity) of a cell.