An electronic smoking device and a method for sensing an aerosol during a puff action to the electronic smoking device, the electronic smoking device has an aerosol sensing unit (100) containing a light intensity detector (11, 12) to detect light reflected by an aerosol moving though the aerosol sensing unit (100). A flow speed of the aerosol is derived based on the light intensity detected and a pressure condition within the aerosol sensing unit (100) detected by a pressure sensor.