A single-blade razor can only cut what’s visible at the surface of the skin. A 5-blade razor can go so much further.
The first blade starts the job. It cuts the hair and, in the process, gently lifts it from the skin. Before the hair has time to fully withdraw, the next blade comes along and cuts it further down.
This process is called ‘hysteresis’ and was discovered in the late 1960s when Gillette was developing its first multi-blade razor, Gillette Contour (also known as Gillette Atra).