Injection head for a fluid substance intended to be injected into an injection site into the body by passing through the skin barrier, said head allowing, prior to the injection, the monitor of the presence of a liquid originating from the injection site and the characterization of said liquid, the injection head comprising a connection body intended to be connected to a reservoir, the pressure of which can be controlled, said reservoir being intended to contain the fluid substance to be injected, said connection body being extended by a hollow tube intended to communicate with the reservoir outlet, the tube having a distal end and a needle that is slidably mounted in a guide channel passing through the connection body, said needle having a pointed distal end, said hollow tube or said connection body having at least one zone for monitoring and characterizing the liquid coming from the injection site, characterized in that the hollow tube communicates with the reservoir outlet via an injection channel passing through the connection body, said injection channel having an end emerging into the guide channel and an end communicating with the reservoir outlet when the injection head is connected to the reservoir, and in that the injection head comprises means for controlling the relative movement of said needle in relation to said hollow tube, between a pricking position in which the pointed end of the needle, which is nested within the hollow tube, projects beyond the distal end of the hollow tube in order to form, with said distal end, a penetrating assembly, and a position for monitoring and characterizing the fluid originating from the injection site via the monitoring and characterization zone, in which the pointed distal end of the needle is positioned in the guide channel, upstream of the end of the injection channel which emerges into the guide channel, and vice versa, said control means comprising a shuttle movably mounted relative to the connection body in order to place the needle in the pricking position or in the position for monitoring and characterizing a liquid coming from the injection site, the needle being secured to the shuttle whereas the hollow tube is secured to the connection body, and resilient return means for the shuttle for placing the needle in the pricking position or in the position for monitoring and characterizing a liquid originating from the injection site. characterized in that the hollow tube communicates with the reservoir outlet via an injection channel passing through the connection body, said injection channel having an end emerging into the guide channel and an end communicating with the reservoir outlet when the injection head is connected to the reservoir, and in that the injection head comprises means for controlling the relative movement of said needle in relation to said hollow tube, between a pricking position in which the pointed end of the needle, which is nested within the hollow tube, projects beyond the distal end of the hollow tube in order to form, with said distal end, a penetrating assembly, and a position for monitoring and characterizing the fluid originating from the injection site via the monitoring and characterization zone, in which the pointed distal end of the needle is positioned in the guide channel, upstream of the end of the injection channel which emerges into the guide channel, and vice versa, said control means comprising a shuttle movably mounted relative to the connection body in order to place the needle in the pricking position or in the position for monitoring and characterizing a liquid coming from the injection site, the needle being secured to the shuttle whereas the hollow tube is secured to the connection body, and resilient return means for the shuttle for placing the needle in the pricking position or in the position for monitoring and characterizing a liquid originating from the injection site.