Local anesthesia works by reversibly inhibiting the propagation of nerve signals in a specific body area. The first local anesthetic was cocaine, discovered in 1860. Local anesthetics are classified as esters or amides based on their chemical structure and method of metabolism. They work by blocking the influx of sodium ions through nerve cell membranes, preventing nerve depolarization. Factors like pH, lipophilicity, and vasoconstrictors affect their potency and duration of action. Common techniques for administering local anesthesia include infiltration, nerve blocks, epidurals, and spinal anesthesia. Potential side effects include both local and systemic toxicity.