Microplastics are small plastic particles in the environment that are generally between 1 and 5 mm (0.039 and 0.197 in). They can come from a variety of sources, including cosmetics, clothing, and industrial processes. Two classifications of microplastics currently exist: primary microplastics are manufactured and are a direct result of human material and product use, and secondary microplastics are microscopic plastic fragments derived from the breakdown of larger plastic debris. Both types are recognized to persist in the environment at high levels, particularly in aquatic and marine ecosystems. Because plastics do not break down for many years, they can be ingested and incorporated into the bodies and tissues of many organisms. The entire cycle and movement of microplastics in the environment is not yet known, but research is currently underway to investigate this issue.