If the problems are severe, perhaps the foundation needs attention. Often cracks appear in the grout between the wall and bathtub or sink. Grout should be kept in good repair to keep water out, because water can damage the walls and house frame. The crack also catches dirt and looks terrible. Grout comes in powder or premixed form and must be mixed with water in small amounts.
Plastic sealer comes in a tube and looks like toothpaste.
It is easier to use than grout but costs more. Read directions on the package before you begin your project. How To Prepare the Surface Remove the old filler from the crack. Wash the surface to remove soap, grease, and dirt. Dry the surface well before you make repairs.