Avoidance of trauma to the ear canal will prevent many cases. Many doctors discourage the use of Q-tips and most other objects to clean the ear canal. Keeping the ear canal dry and free of wax will help prevent some cases. A simple eardrop solution can work well to keep the ear canal dry. Avoidance of neomycin-containing drugs may prevent some cases as well.
Most cases do not cause any long-term effects. But where they do, the main long-term effect would be continued thickening of the skin of the ear canal to the point where the ear canal is blocked and hearing loss occurs.
There are no risks to others.