Why do Quelli people wear masks in terms of quality and effect?

According to the Quayle people themselves, Quayle people live on immigrant ships, have been in a sterile environment for a long time, and their immune system has deteriorated, so they can only walk outside in protective clothing. It is said that if the protective clothing is broken, it may be life-threatening. .............. bioware said Natalie in mass effect 3 would take off her mask. Now the so-called real pictures on the Internet are all made by netizens themselves.