Many studies suggest that genes, environment, and age contribute to the onset of late-life neurodegenerative disease like amyotrophic lateral sclerosis. Epidemiological studies have shown correlations between environmental chemical exposure and neurodegeneration, but no direct and causal relationships have been established. Conversely, there may be environmental actors that suppress or delay neurodegeneration outcomes. The human body is the natural habitat for many microbes, including hundreds of bacterial species referred to as the microbiota.