Considering the number of people that move through an airport in a day, the number of germs they bring along with them would make anyone cringe. You may want to use your layover time to rest up and shower, which is now made possible in most major airports by small accommodations within airport terminals. These cabins, usually featuring a bed, shower, and TV, can be rented for at least four hours at a time.
If these cabins aren't available at your airport, or if you need a little more space, you might consider an airport hotel near by. For some peace and quiet, and the chance to wash up, it might be worth it—plus, most hotels offer free shuttle service to and from the airport, making it easy and convenient for you.
In either of these situations, it's recommended that you plan ahead and make reservations, rather than walking in and requesting a room. It'll be cheaper and smoother if you take care of everything beforehand.