Why was malaria called "bad air" in earlier times?

The term "malaria" originates from the Italian words mala aria, meaning "bad air". In earlier times, the disease was associated with swamps and marshes, where people observed that illness often occurred in areas characterized by stagnant water and foul odors.123

Because the true biological mechanisms of infectious disease were unknown, physicians and the public relied on miasma theory, which attributed various illnesses to the inhalation of "miasmas"—noxious vapors or pollutants arising from decaying organic matter and stagnant environments. Consequently, the disease was named for this perceived cause, as it was believed that breathing these vapors directly disrupted the body's normal functioning.23

It was not until the late 19th century that scientific advancements in microbiology and the discovery of the parasite transmission cycle via mosquitoes disproved the miasmatic explanation, shifting medical understanding toward the germ theory of disease.23