How to distinguish the front and back of a white mask?

How to distinguish the front and back of a white mask?
According to the degree of smoothness, the outward-facing part of the mask is mostly smooth because of its water-blocking function; while the inner-facing part is selected to be a material with good breathability, which is close to the skin and conducive to breathing.
Extended information:
Precautions for use:
1. Duration of use
From the point of view of human physiology, blood circulation in the nasal mucosa is very strong, and the channels in the nasal cavity are very tortuous. The nose hairs constitute a filtering "barrier". When air is inhaled into the nostrils, the airflow forms a vortex in the tortuous channel, which heats the airflow into the nasal cavity.
Some tests have shown that when cold air at minus 7 ° C is drawn into the lungs through the nasal cavity, the airflow has been heated to 28.8 ° C, which is very close to the temperature of the human body. If you wear a mask for a long time, the nasal mucosa will become fragile and lose the original physiological function of the nasal cavity, so you cannot wear a mask for a long time.
2. Cleaning and maintenance
The outer layer of the mask often accumulates a lot of dust, bacteria and other dirt in the outside air, and the inner layer blocks the exhaled bacteria and saliva. Therefore, the two sides cannot be used interchangeably, otherwise the dirt contaminated by the outer layer will be directly attached When inhaled into the face, it becomes a source of infection. When the mask is not worn, it should be folded and placed in a clean envelope, and the side close to the nose and nose should be folded inwards, and it should never be stuffed into the pocket or hung around the neck.
3. Handle properly
Daily use of masks should be properly handled. Masks used by patients or used during care should be placed in a lined container in the patient room before being processed.