Fuel injector with deformable needle

A fluid injector comprises a housing, an actuator unit and a valve body. The valve body has a needle (22) and a cartridge (21) with a recess, which takes in the needle (22) and which comprises on one of its ends a seat plate (213), that comprises a needle seat (2132) for the inward-opening needle (22), with the needle (22) further comprising a seat part (221) with a sealing area (222), that is destined to rest on the needle seat (2132) if it is pushed against the needle seat (2132), with the seat part (221) comprising a cavity radially inwards and in proximity to the sealing area (222).