Long-term studies of patients treated without surgery for disc herniation are underway. Some of the results indicate changes occur in the disc for up to two years after the initial injury.
Serial MRIs (several taken over time) show a gradual reduction of the bulging disc. Patients seem to improve over time at about the same rate no matter what size the disc was to start. Some patients had painful symptoms and some didn't. Some patients had more than one disc involved. None of these factors seem to affect the healing disc.
Age seems to be the only deciding factor. Younger patients seem to have the worst results but it's not clear yet why this occurs. It may be linked to a more active lifestyle in the younger adults.