Made by a pharmacist whose son was sick with croup, Vicks VapoRub saw skyrocketing sales during the 1918 Spanish flu outbreak.

For most people, memories of childhood coughs and colds are synonymous with a menthol-smelling ointment in a dark blue jar with a turquoise cap.

For more than a century, Vicks VapoRub has been a household name across continents. How it became one has roots in the Spanish flu pandemic in the early 20th century.