How deep can a topical anesthetic be effective on tissues?

Topical anesthetics are designed to provide localized pain relief on the surface of tissues, primarily affecting the mucous membranes and superficial layers. The effective penetration depth of a topical anesthetic typically ranges from 2 to 3 mm. This limited depth is sufficient for procedures that require desensitization of the immediate surface area where an injection or other minor intervention will occur.

Topical anesthetics work by reversibly blocking nerve conduction in the area where they are applied, which is most effective in the upper layers of the skin or mucosal tissue. Beyond this range, the anesthetic may not achieve sufficient nerve block to provide adequate pain relief, which is why deeper penetration (like in the options that suggest 4 mm or more) would not typically be effective with topical agents. That is why the provided answer accurately reflects the practical depth of topical anesthetics in clinical use.