In Taoism, it is a way to pray for the blessing of the gods, which is usually used to pray for the peace, health and wealth of the gods. You must use yellow paper or red paper when you show your face, because in the traditional culture of China, yellow and red represent auspiciousness and sacredness.
It should be noted that it is not a scientific phenomenon, and its authenticity has not been widely recognized. Therefore, when using this form of prayer, we should maintain a rational and scientific attitude and not be overly superstitious.