To become progressively worse in condition or quality.
“The condition of the road has continued to deteriorate since last winter.”
“My symptoms began to deteriorate after using the product as directed.”
This verb is useful in CELPIP Writing Task 1 complaint emails describing a worsening problem, such as a product or living condition that has gotten worse over time. Using 'deteriorate' instead of 'get worse' adds a more formal, precise tone to your complaint.
Synonyms: worsen, decline, degrade