Nail onychomycosis, or fungus infection, is typically caused by a fungus called dermatophytes, but may also be caused by yeasts and molds. These microscopic organisms invade the skin through tiny invisible cuts or through a small separation between the nail and the nail bed. Under conditions of warmth and moisture, the fungi grow and spread. The infection begins as a white or yellow spot under the tip of the nail, and as it spreads deeper into the nail, causes unsightly and potentially painful nail discoloration, thickening and the development of crumbling edges. Onychomycosis occurs more commonly in toenails than in fingernails because toenails are often confined in a dark, warm, moist environment inside shoes where fungi can thrive. Toenail fungus affects approximately 23 million people in the US - about 10% of all adults.

Potential complications of onychomycosis include pain in the nails, permanent damage to the nails, development of other serious infections that can spread beyond the feet for individuals with a suppressed immune system due to medication, diabetes or other conditions, such as leukemia and AIDS.

Nail fungus can be difficult to treat, and repeated infections are common. Currently available treatments for onychomycosis include oral antifungal medications, antifungal lacquer, and topical medications, surgical nail removal and photodynamic therapy. There is no perfect cure for toenail fungus. Even the most effective oral medications are successful only about half of the time, and topical medications are successful less than 10% of the time. Recently, research has found laser therapy to show promise as a novel alternative treatment for toenail onychomycosis. Unlike medication-driven treatments for toenail fungus which can have many side effects including serious ones such as liver toxicity, laser therapy presents minimal to no risk of side effects. Laser therapy is applied to toenail onychomycosis by shining a laser light through the toenail into the tissue below. The laser light vaporizes the fungus while leaving the skin and surrounding healthy tissue unharmed.

Low level laser therapy operates under the principle of photochemistry with a photoacceptor molecule absorbing the emitted photons and inducing a biological cascade. Like our eukaryotic cell, fungi contain the highly complex organelle the mitochondria, which is responsible for the manufacturing of the energy molecule adenosine triphosphate (ATP). Within the inner mitochondrial membrane is cytochrome c oxidase, an identified photoacceptor molecule. It is believed that laser therapy could perhaps provide a means to photo-destroy the fungi responsible for onychomycosis (OM) by inducing the release of highly reactive superoxides. Moreover, laser therapy has been shown to promote superoxide dismutase (SOD), a process responsible for the destruction of foreign invaders. Extracellular release of low levels of mediators associated with SOD can increase the expression of chemokines, cytokines, and endothelial leukocyte adhesion molecules, amplifying the cascade that elicits the inflammatory response. The physiologic function of hydrogen peroxide, superoxide anion, and hydroxyl free radical is to destroy phagocytosed microbes. By enhancing the natural processes of the immune system and impacting the structural integrity of the fungi strain, it is believed that laser therapy may provide a means for clinicians to effectively treat OM without the onset of any adverse events.