Testicular inflammation, also known as orchitis, often develops when bacteria from an existing urinary tract infection spread to the testicle. In young adults, the primary cause is sexually transmitted infections (STIs), whereas in older men, the progression of a prostate-related urinary tract infection to the testicle is a leading cause. One of the most significant viral causes is mumps orchitis, characterized by inflammation of one or both testicles in patients who have had mumps.

Factors that increase the risk of orchitis include:

* Use of a urethral catheter (probe)
* Benign Prostatic Hyperplasia (BPH)
* Recurrent urinary tract infections
* Not being vaccinated against mumps or not having had mumps previously
* Having multiple sexual partners
* Exposure to unhygienic environments