A piston for a reservoir of a dispenser of a fluid product without air intake and presenting a central axis X includes both sealing means and also guiding means. The sealing means extend in a plane orthogonal to the axis X and define a single external sealing line in a closed loop, distal from the axis X, capable of coming into contact with an inner wall of the reservoir 10. The guiding means include a base from which extends one or more tabs with free ends defining external guide points, distal from the axis X, capable of coming into contact with the inner wall of the reservoir.

A squeeze pump includes a container body with an elastic deformability, and an accommodation cavity is formed inside the container body, a piston slidably provided inside the accommodation cavity and in a sealing fit with the container body, where the piston is configured to divide the accommodation cavity into a medium cavity and a gas cavity that do not communicate with each other, the medium cavity is configured to accommodate a pasty substance, and the medium cavity is in communication with a paste outlet, and a one-way inlet valve in communication with the gas cavity and configured to control that air enters into the gas cavity in one direction and avoid an escape of the air from the gas cavity.

A squeeze pump includes a container body with an elastic deformability, and an accommodation cavity is formed inside the container body, a piston slidably provided inside the accommodation cavity and in a sealing fit with the container body, where the piston is configured to divide the accommodation cavity into a medium cavity and a gas cavity that do not communicate with each other, the medium cavity is configured to accommodate a pasty substance, and the medium cavity is in communication with a paste outlet, and a one-way inlet valve in communication with the gas cavity and configured to control that air enters into the gas cavity in one direction and avoid an escape of the air from the gas cavity.