The phrase "to become life threatening" means that a condition, situation or disease has become so severe that it could result in the loss of life. Full definition
Puppies do not have strong immune systems so the smallest illness can become life threatening very quickly. (healthguidance.org)
These problems can lead to dental infection that can spread to the heart, kidneys and other organs, and possibly become life threatening. (langleyanimalclinic.ca)
I remind pet owners that an untreated dental infection can spread to the heart, kidneys and other organs, and suddenly become life threatening. (compassionatecareveterinaryhospital.com)