One of the most important aspects to consider when we light the bathroom is the degree of safety provided by the lamp against dust or water. This is indicated by the Index of Protection (IP) code, which is identified by two numbers: the first number indicates protection against dust and the second number indicates protection against water. The higher the number, the greater the protection. The following diagram shows you which is the best Index of Protection code according to the different areas of your bathroom. 
Z1 - Zone 1: General Lighting. For this zone an IP44 will be sufficient
Z2 - Zone 2: Mirror area. As in Zone 1, we will use IP44
Z3 - Zone 3: Space near the bathtub. In this case, we will need IP65 lamps, to be protected against splashes and jets of water.
Z4 - Zone 4: Shower area. This is the wettest area so we'll have to install IP67 lamps that are fully protected from dust and water. Check our 10 tips to light the bathroom or visit How to light your bathroom in a functional and decorative way.