A swollen, painful left testicle has several possible causes, ranging from infections and fluid buildup to conditions that need emergency surgery within hours. The left side is actually more commonly affected by certain conditions like varicoceles due to differences in how blood drains from each testicle. While many causes are treatable and not dangerous, sudden severe pain that comes on within minutes is a medical emergency.
Sudden Severe Pain: Testicular Torsion
If your pain started abruptly and is intense, the most urgent possibility is testicular torsion, where the testicle twists on the cord that supplies its blood. This cuts off circulation and can permanently damage the testicle if not surgically corrected quickly. The traditional teaching is that you have a 6 to 8 hour window, but a systematic review of survival data shows a more detailed picture: salvage rates are about 90% if surgery happens within 12 hours, drop to 54% between 13 and 24 hours, and fall to roughly 18% beyond 24 hours.
Torsion typically causes sudden, severe pain on one side, often accompanied by nausea or vomiting. The affected testicle may sit higher than usual or lie at an abnormal angle. The scrotum often becomes red and swollen rapidly. This happens most often in teenagers and young men, though it can occur at any age. If this sounds like what you’re experiencing, go to an emergency room immediately. Doctors use an ultrasound with blood flow imaging to confirm torsion. In cases of torsion, the scan shows absent blood flow and twisted vessels, while inflammatory conditions show increased blood flow.
Infection and Inflammation
Epididymitis, an infection of the coiled tube behind the testicle, is one of the most common causes of scrotal pain and swelling in adult men. Unlike torsion, the pain typically builds gradually over days rather than striking all at once. You may notice tenderness that starts at the back of the testicle and spreads, along with warmth, redness, and possibly a low fever. Some men also have burning during urination or unusual discharge, though urethritis is frequently asymptomatic even when an STI is the underlying cause.
The bacteria responsible depend largely on age and sexual activity. In sexually active men under 35, sexually transmitted organisms are the most common culprits. In older men, the infection more often comes from urinary tract bacteria, particularly when there’s an underlying issue like an enlarged prostate that prevents the bladder from emptying completely. Treatment involves a course of antibiotics targeted to the likely organism, along with rest, scrotal support, and anti-inflammatory pain relief. Most men feel significantly better within a few days of starting treatment, though full resolution can take several weeks.
When the infection spreads to the testicle itself, it’s called orchitis. Viral infections, most notably mumps, can also cause orchitis without involving the epididymis first.
Fluid Buildup and Cysts
A hydrocele is a collection of fluid around the testicle that causes painless or mildly uncomfortable swelling. It often develops slowly, and you may notice the scrotum feels heavier on one side. Hydroceles are usually not dangerous, but they can grow large enough to become bothersome. A simple office test can help distinguish them from solid masses: when a light is held behind the scrotum, fluid-filled swellings glow as light passes through, while solid masses block the light.
A spermatocele is a similar fluid-filled cyst, but it forms on the epididymis rather than around the testicle itself. These are typically small, painless, and found incidentally, though larger ones can cause a dull ache or a feeling of heaviness. Neither hydroceles nor spermatoceles are cancerous, and many don’t require treatment unless they’re causing discomfort.
Hernia Extending Into the Scrotum
An inguinal hernia occurs when tissue from the abdomen pushes through a weak spot in the lower abdominal wall, and it can extend all the way into the scrotum. This typically shows up as a bulge in the groin or scrotum that may come and go, often getting more noticeable when you stand, cough, or strain. You might feel heaviness, a burning sensation, or a dull ache in the area.
Most inguinal hernias aren’t emergencies, but they become one if the hernia gets trapped outside the abdominal wall and can’t be pushed back in. A strangulated hernia cuts off blood supply to the trapped tissue and causes sudden, severe pain, nausea, vomiting, fever, and redness over the bulge. A hernia bulge that was previously reducible but suddenly becomes firm and painful needs emergency care.
Varicocele
A varicocele is an enlargement of the veins inside the scrotum, similar to varicose veins in the legs. It occurs on the left side in roughly 80 to 90% of cases because of how the left testicular vein connects to the circulatory system at a sharper angle, creating more pressure. Varicoceles usually cause a dull, aching pain that worsens with prolonged standing or physical activity and improves when you lie down. You may feel something that resembles a “bag of worms” above the testicle. Many varicoceles don’t need treatment, but they’re worth evaluating because large ones can affect fertility over time.
Testicular Cancer
The most common first sign of testicular cancer is a hard lump or swelling on the testicle itself. Most testicular cancers are painless or only mildly uncomfortable, which distinguishes them from infections and torsion. Some men notice a dull ache in the lower belly or groin, or a general feeling of heaviness in the scrotum. Testicular cancer is most common between ages 15 and 45, though it can happen at any age.
Any firm, painless lump on the testicle that doesn’t go away within a week or two should be evaluated with an ultrasound. The good news is that testicular cancer has very high cure rates even when caught at later stages, and outcomes are even better with early detection.
Chronic Pain Without a Clear Cause
Some men experience ongoing testicular pain for months without any infection, mass, or structural problem showing up on exams or imaging. Research has found a strong link between this type of unexplained scrotal pain and overactivity in the pelvic floor muscles. In one study of 41 men with chronic testicular pain and no identifiable cause, 88% had abnormally high resting tension in their pelvic floor muscles, and 93% had at least one other symptom of pelvic floor dysfunction, such as urinary frequency, difficulty with bowel movements, or pain during sex. The testicle shares nerve pathways with the pelvic floor, hip, and ureter, so tension or dysfunction in any of those areas can produce referred pain that feels like it’s coming from the testicle. Pelvic floor physical therapy is the primary treatment for this pattern.
Men who’ve had a vasectomy are another group that sometimes develops chronic testicular pain. Post-vasectomy pain syndrome affects roughly 1 to 2% of the approximately 500,000 men who undergo the procedure each year in the U.S., though some estimates run as high as 15%. The pain is typically constant or intermittent, lasting more than three months after surgery, and may include discomfort during ejaculation or erections. A tender or full-feeling epididymis is a common finding.
What Happens During Evaluation
A doctor will start with a physical exam, checking for lumps, tenderness, swelling, and the position of the testicle. They’ll likely ask when the pain started, how quickly it developed, whether anything makes it better or worse, and whether you have urinary symptoms or fever.
The most important diagnostic tool is a scrotal ultrasound with color Doppler imaging. This painless scan shows the internal structure of the testicle and, critically, the blood flow patterns. Absent blood flow with twisted vessels points to torsion. Increased blood flow indicates inflammation or infection. Solid masses versus fluid collections are clearly visible, helping distinguish tumors from hydroceles or cysts. The scan takes about 15 to 20 minutes and gives clinicians most of the information they need to determine the cause and start the right treatment.