It's peak cold and flu season, and mucus is making many of our lives miserable. But despite being a little icky, phlegm gets a bad rap. This germ-fighting goo contains cells and chemical compounds that help us power through a cold.
You can also think of mucus as a traffic light for your health - what turns up in our used tissues can be a useful clue about the inner workings of our immune systems.
Reactions decodes the mysteries of mucus in its latest video:
Explore further: Protection of the mouse gut by mucus depends on microbes