病从口入

Illness enters by the mouth (idiom). Mind what you eat! / fig. A loose tongue may cause a lot of trouble.

from / through / via / to follow / to obey / to engage in (an activity) / never (in negative sentence) / (Taiwan pr. [zong4]) retainer / assistant / auxiliary / subordinate / related by common paternal grandfather or earlier ancestor

mouth / classifier for things with mouths (people, domestic animals, cannons, wells etc) / classifier for bites or mouthfuls

illness / CL:場|场[chang2] / disease / to fall ill / defect

to enter / to go into / to join / to become a member of / to confirm or agree with / abbr. for 入聲|入声[ru4 sheng1]

Illness enters by the mouth, trouble comes out by the mouth (idiom). A loose tongue may cause a lot of trouble.