Hunger is the feeling of wanting to eat. Ghrelin is a hormone that makes people feel hungry. The opposite of hunger is called "satiety" or "fullness". Leptin causes this feeling. People can survive weeks without eating, but they will start to feel hungry after they have not eaten for a few hours. Hunger is generally considered quite uncomfortable. People who have eaten food usually will feel less hungry, or not hungry at all. People can live longer without food than without water.