Viruses and bacteria are easily introduced into the body through the air when we breathe or eat.
As soon as viruses and bacteria enter the body, they start trying to multiply. As soon as they multiply, the human body becomes ill. When the body is healthy, viruses and bacteria can be easily suppressed, but when the body is weak and resistance is weakened, viruses and bacteria cannot be suppressed and continue to multiply in the body.
If viruses and bacteria multiply in the nose, they can cause a disease called rhinitis; if in the bronchi, bronchitis; if in the stomach, gastritis; and if in the intestines, enteritis. When the symptoms of these diseases are still mild, it is called a cold.