Hair-cutting unit for use in a hair-cutting appliance , comprising - an external cutting member having hair-entry openings in a cutting track surface , - an internal cutting member having at least one hair-cutting element and being movable with respect to the external cutting member , and - a skin-supporting structure having a skin-supporting surface for contacting a portion of skin to be subjected to a hair-cutting action, wherein the external cutting member is displaceable relative to the skin-supporting structure , characterized in that the hair-cutting unit further comprises - a safety mechanism which is designed to enable stepped variation between at least two discrete stages of a level (l c ) of the cutting track surface with respect to a level (l s ) of the skin-supporting surface , in relation to pressure exerted by the external cutting member on the skin, wherein the safety mechanism is configured - to maintain a default stage as long as the pressure exerted by the external cutting member on the skin is below a predefined threshold value, the default stage involving a most protruding position of the external cutting member in which the cutting track surface protrudes with respect to the skin-supporting surface to a maximum extent, and - to instantaneously set a retracted stage the moment the pressure exerted by the external cutting member on the skin increases and passes the predefined threshold value, the retracted stage involving a less protruding position of the external cutting member and a retracted position of the cutting track surface with respect to a position of the cutting track surface in the default stage. - an external cutting member having hair-entry openings in a cutting track surface , - an internal cutting member having at least one hair-cutting element and being movable with respect to the external cutting member , and - a skin-supporting structure having a skin-supporting surface for contacting a portion of skin to be subjected to a hair-cutting action, wherein the external cutting member is displaceable relative to the skin-supporting structure , characterized in that the hair-cutting unit further comprises - a safety mechanism which is designed to enable stepped variation between at least two discrete stages of a level (l c ) of the cutting track surface with respect to a level (l s ) of the skin-supporting surface , in relation to pressure exerted by the external cutting member on the skin, wherein the safety mechanism is configured - to maintain a default stage as long as the pressure exerted by the external cutting member on the skin is below a predefined threshold value, the default stage involving a most protruding position of the external cutting member in which the cutting track surface protrudes with respect to the skin-supporting surface to a maximum extent, and - to instantaneously set a retracted stage the moment the pressure exerted by the external cutting member on the skin increases and passes the predefined threshold value, the retracted stage involving a less protruding position of the external cutting member and a retracted position of the cutting track surface with respect to a position of the cutting track surface in the default stage. <EOS>