Usually it is a combination of biological factors(genetics), environmental and social factors that can create mental health conditions. There are some sorts of disorders that are more biological like autism which people are born with...but then one with that disorder still can have good mental health so not sure those sorts of things count as mental health conditions.

But for things like depression, anxiety, ect its a combination of various factors that can cause it. I wouldn't say its something you catch like a cold or anything like that.