Piano keys will get dirty, that's a fact of life. Skin oils and sweaty fingers help dust and dirt bind to the keys. It doesn't matter, if you diligently clean your hands every time you sit down to play, which by the way you should, over time they will get dirty.
But that is not really much of a problem, because piano keys are very easy to clean. The whole process might be a bit tedious, but it's important - you will feel better while playing and it will keep your piano in good shape.
How To Clean Piano Keys
What do you need to clean piano keys? You will need:
soft cloth
gentle soap
warm water
persistence
Piano keys are usually made of fake ivory, which means they are essentially plastic. Just don't use anything abrasive.
To clean just dampen a soft cloth with warm water and some sort of gentle soap (or you can use a glass cleaner). Wring it out until it's not dripping anymore. Be careful not to drip anything into the keys. Remember, use damp, not soaked cloth. Clean each key individually. Yes, it takes time and patience, but in the end you will have your keys sparkling like new.