It is recommended that you have your caulking replaced on a regular basis in order to protect your home from water damages caused by a shower leak. Depending on usage you may need to re-caulk every one to five years. Caulking is a flexible material bridging the gap between two separate surfaces that meet, such as tile to tile, tub to tile, and where the drywall and tile, or fiberglass unit meet. Many installers simply grout these areas and leave it at that. Problems arise when the inflexible cement based grout cracks due to inevitable movement and water penetrates the surface. The backer board behind the tile then wicks the water up and becomes saturated over time leading to mold and deterioration.