How do local anesthetics numb a specific part of the body?

Local anesthetics numb a specific part of the body by temporarily blocking the conduction of nerve impulses along peripheral sensory nerves.1

When administered—typically via injection or topical anesthesia—these drugs penetrate the fatty membrane of nerve fibers. Once inside, they block ion channels that normally allow sodium ions to flow during nerve excitation. By preventing this movement of ions, the anesthetic stops the electrical currents required to transmit pain signals to the spinal cord and brain.1

The effectiveness of this process is selective; thinner nerve fibers, which often carry pain sensations, are blocked more easily than thicker ones. Because the drug is applied directly to the nerves innervating a specific region, the resulting loss of sensation is restricted to that area, allowing for procedures such as dental work or skin repair while the patient remains conscious.1