Blushing is controlled by the sympathetic nervous system. This is the same system that controls panic “flight-or-fight" responses. Blushing is an involuntary reaction, which means your body does it without you even thinking about it.
Adrenaline does unusual things to your body, which are all part of the fight-or-flight response. When your body releases adrenaline, it causes your breathing and heart rate to increase. This prepares your body to run from danger. Adrenaline also causes your pupils to grow larger, which helps you take in more visual information than usual.
While scientists understand the physical process of blushing, they're still not sure what purpose, if any, it serves. Some researchers think it is the body's automatic way of admitting guilt over something…and apologizing for it.
For example, imagine you are helping your parents wash the dishes and you accidentally break a plate. Even before you have a chance to apologize, blushing would be your body's way of letting your parents know it was an accident and you feel bad.