Pain may increase temporarily due to irritation of the nerves in the spine. The steroid injection introduces fluid into a compressed space, the epidural space, where inflammation may have already been present.
This 2021 study looked at how long localized pain at the injection site lasted after an epidural. Pain for most people involved in the study seemed to resolve in less than 48 hours, with a few people reporting pain took under 3 months to resolve.
Researchers speculated that some factors such as positioning during the epidural and age may play a role in post-op pain. The authors noted that pain occurred more in those under age 50.