Natural stone marble can be used in showers with several caveats. Marble is a soft stone that is very porous with natural fissures. Depending on the iron level of the marble (which varies widely), consistent exposure to moisture and humidity can cause discoloration. Therefore, marble must be sealed before use and resealed on a regular basis. Avoid using acid-based cleaners as they cause etching and compromise sealants. For those who feel this sounds like too much work, marble look tile would be a better option for you. With porcelain, none of these precautions apply as it is impervious to water, stain-resistant, scratch-resistant, and easily maintained.