A retractable safety syringe may comprise a needle, needle holder, syringe body, and a plunger. A proximal portion of the body and a piston of the plunger may define a variable vacuum compartment. A through hole pneumatically connecting ambient air and the variable vacuum compartment may be formed through a thumb platform and rigid shaft of the plunger for allowing air to escape out of the variable vacuum compartment when a piston of the plunger is traversed toward the retracted position and allow air to be introduced into the variable vacuum compartment when the piston is traversed toward the engaged position. A retraction force may be created by the variable vacuum compartment by covering an entrance of the through hole and traversing the piston to the engaged position. At the engaged position, the piston may engage the needle holder and the retraction force may retract the piston, needle holder and needle into the syringe body to prevent accidental needle pricking and needle reuse.
