Germs need an alkaline environment in which to thrive and multiply, making lemon juice a natural enemy due to its rich acid content. One oz. of pure lemon juice contains 1.44 g of citric acid.
Lab studies support the effectiveness of lemon juice as an antibacterial. The Leptospirosis Information Center finds the citric acid in lemon juice a suitable substitute for chemical cleaners. Leptospirosis is a bacteria that can cause disease in animals and humans, and is not tolerant of acids.
In a 1993 test to determine the effectiveness of lemon juice in purifying water in Argentina, the National Center for Biotechnology Information reported a significant reduction in the v. cholera bacterium as long as enough lemon juice was used to lower the water's alkalinity levels, which encourage bacterial growth.
Because of its properties as a germ killer, lemon juice can serve as an effective and natural alternative to household disinfectants, as well as a natural freshener.