These fine white dots on the buccal mucosa are seen in the early stages of measles infection. They resemble scattered grains of salt on a red background.
These spots appear before the skin exanthem and fade as the skin rash develops. Their identification can allow early diagnosis and isolation, which is imperative to prevent the spread of this contagious infection.
Image credits: https://usmlepathslides.tumblr.com/post/21538802490/koplik-spots-on-buccal-mucosa-in-rubeola-note-the/amp