well there are many people whom believe that if you clean the hatching egg you have a greater risk of rubbing bacteria into the egg and that can cause the egg not to develop or die. We had a few eggs that had a lot of dirt on them and we didn't clean them, they didn't hatch or develop at all. Because the eggs do have pores it is my opinion that the bacteria thing is possible and for that reason we don't clean the eggs we just put them in the incubator and see what happens. Out of three batches of doing this none of the dirty eggs have ever hatched. So I guess just from my experince if I ever have a dirty egg I am going to try to clean it with a damp paper towel but not really expect anything to really happen.