Louis Sigurd Fridericia (24 February 1881 – February 1947) was a Danish hygienist and professor born in Copenhagen.
Fridericia's family moved to Denmark in the 1750s and took as a name a form of the name of the Jutland town, Fredericia, where they settled. He attended the University of Copenhagen and graduated in medicine in 1906.
He became a physician that year and received further education from Christian Bohr (1855-1911) in Copenhagen, Ernst Leopold Salkowski (1844-1923) in Berlin, Georges Dreyer (1873-1934) and Francis Gotch (1853-1913) at Oxford.
In Copenhagen, he was an assistant at the institutes of physiology, bacteriology and general pathology, and assistant physician at the Rigshospitalet, the Kommunehospitalet and the Bispebjerg Hospital.
He was habilitated in 1910 and in 1918 was appointed Professor of Hygiene.