During the time of a pandemic and the existence of a highly contagious corona-virus, many scientists recommended wearing a mask. Les us assume that wearing a mask can limit the spread of the virus. Is wearing a mask an externality? Positive or negative? How about not wearing a mask? Explain your answers.

During the time of a pandemic and the existence of a highly contagious corona-virus, many scientists recommended wearing a mask. Les us assume that wearing a mask can limit the spread of the virus. Is wearing a mask an externality? Positive or negative? How about not wearing a mask? Explain your answers.