It can also be caused by. 1  chemicals. 2  contact lens wear(https://www.cdc.gov/contactlenses/index.html) (especially wearing lenses overnight) 3  foreign bodies in the eye (like a loose eyelash) 4  indoor and outdoor air pollution caused, for example, by chemical vapors, fumes, smoke, or dust. 5  fungi.
Voluntarism, sometimes referred to as voluntary action, is the principle that individuals are free to choose goals and how to achieve them within the bounds of certain societal and cultural constraints, as opposed to actions that are coerced or predetermined. 1 Volunteerism. 2 Varieties.
It is certainly, however, not a commitment that is taken on for financial gain. More likely, altruism is the motivating factor behind the choice to become a volunteer, whether paid or unpaid. On the other hand, an internship is work that we take on in order to learn more about a given profession.