When astronauts head back to the moon, one of their primary concerns will be the dust. No matter how much they tried to brush off the powder when they came back inside the shelter of the LM, some still stuck. Then it tended to get everywhere -- hair, experiments, even in astronauts' mouth. On Apollo 17, one astronaut reported getting a sort of hay fever from the powder. Several astronauts have reported that the dust smells like gunpowder, but the chemical reactions causing this are under debate.