Name a health behavior that could increase someones susceptibility to an illness is this behavior easy to change why/why not

An easy example is poor dietary choices. Things such as skipping meals, eating irregularly, eating unhealthy food, can all make a person susceptible to various illnesses, and it is rather easy to change because a person can make it as easy as setting an alarm clock for every meal and purchasing healthy food instead of non-healthy kind.

What are the choices?