Possible causes of left testicular pain: 1. Varicocele on the left side can cause chronic pain in the left testicle, which is aggravated after activity and can be relieved after rest. The scrotum is slightly enlarged when touched by hand, and thickened and tortuous vascular tissues can be felt in the scrotum and around the testicles. Further ultrasound examination of the spermatic vessels and scrotal ultrasound examination are needed to confirm the diagnosis. 2. Testicular pain can be caused by left testicular inflammation or epididymitis. The pain is usually acute and can be accompanied by a significant increase in the size of the testicle and epididymis or by redness and swelling of the scrotal skin, and there may be fever or pain radiating to the groin area. It is recommended that further ultrasound and blood tests be performed to confirm the diagnosis of orchitis and epididymitis. 3. Testicular tumors can appear as swelling and pain in the left testicle, and the texture of the testicle becomes hard and the density becomes high. The pain is chronic and serious patients may have enlarged inguinal lymph nodes, further testicular tumor index examination is needed to confirm the diagnosis.