This is a good question, as they say, disease enters by the mouth, the main point is hygiene, there are many germs on the hands, and if you don't wash them, when they come into contact with the food, they will eat the germs into your stomach, which greatly increases the chance of getting sick, especially infectious diseases, the most common being the common cold. But the mouth, usually, it only comes into contact with the food and the water (except for a few cases), so it is important to wash your hands in a timely manner, especially if you have a special occupation or work in a special service, as it depends on the situation, you cannot generalize. Of course, if you have a special profession or work in a special service, it's also necessary to wash your mouth, but this depends on the situation and can't be generalized.