(someone's) health (is/has been) deteriorating

"Deteriorating" means "getting worse and worse". You can use it to talk about something that's getting worse and doesn't seem like it's going to get better. Here are some examples of things that "deteriorate":

The nation's economic situation is continuing to deteriorate.

The snow is getting thicker, and road conditions are rapidly deteriorating.

We haven't even been married for a year, and I already feel like our relationship is deteriorating

This phrase appears in these lessons: