What is a mental hygiene issue?

A practice. Here's a reference on the history of the term, "mental hygiene": http://www.Jhsph.Edu/departments/mental-health/about/origins.Html mental hygiene is the set of practices conducive to the preservation of mental health. Those practices have changed over the years, but taking care of physical health , meditation, socializing, taking time for gratitude, etc. Might all be mental hygiene practices.