Having one testicle slightly bigger than the other is completely normal. Most men have some degree of asymmetry, and it’s also common for one testicle to hang lower. The difference is usually small enough that you wouldn’t notice without looking closely. That said, a noticeable or sudden change in size can sometimes point to a condition worth getting checked out.
Normal Asymmetry Is the Default
Your testicles are not identical organs. Just like your hands or feet, they naturally differ slightly in size and position. One hanging lower than the other actually serves a purpose: it prevents them from pressing against each other. If you’ve always had a minor size difference and nothing has changed recently, there’s very likely nothing wrong.
The key question isn’t whether one is bigger. It’s whether something has changed. A testicle that has gradually or suddenly grown larger, feels heavier, or has developed a new lump deserves attention. The sections below cover the most common reasons that happens.
Varicocele: Enlarged Veins in the Scrotum
A varicocele is a swelling of the veins inside the scrotum, similar to a varicose vein in the leg. Blood pools in the veins instead of draining efficiently, which can make one side of the scrotum feel fuller or look larger. Varicoceles affect up to 15% of men and almost always develop on the left side due to the way the veins on that side connect to the rest of the circulatory system.
If you can feel a varicocele, it often resembles a soft, lumpy mass above the testicle, sometimes described as a “bag of worms.” Smaller ones may not be visible but can still be felt. Most varicoceles cause no symptoms at all. Some men notice a dull ache that worsens after standing for long periods or during physical activity. The main medical concern is fertility: roughly 10% to 20% of men diagnosed with a varicocele have difficulty fathering a child, and among men already dealing with fertility problems, about 40% turn out to have one.
Hydrocele: Fluid Around the Testicle
A hydrocele is a collection of fluid in the thin sac that surrounds each testicle. It creates a smooth, painless swelling that can make one side of the scrotum noticeably larger. Hydroceles are common in newborns and often resolve on their own, but adults can develop them too, sometimes after an injury or infection. The swelling usually feels heavy rather than painful. If you shine a flashlight against the swollen area in a dark room, a hydrocele often glows because the fluid allows light to pass through.
Spermatocele and Epididymal Cysts
A spermatocele is a fluid-filled cyst that forms in the epididymis, the coiled tube sitting behind and on top of each testicle where sperm mature. These cysts are benign, painless, and extremely common. They feel like a small, smooth, separate lump near the top or back of the testicle. Because the epididymis itself is naturally bumpier and softer than the testicle, it’s easy to mistake normal anatomy for something abnormal during a self-check. Spermatoceles rarely need treatment unless they grow large enough to cause discomfort.
Infections That Cause Swelling
Epididymitis is an infection or inflammation of the epididymis that causes pain, swelling, and tenderness on one side. It typically comes on over a few days and can make the affected testicle feel noticeably larger. The spermatic cord (the structure running up from the testicle) often becomes tender and swollen too. When the infection spreads to the testicle itself, the condition is called epididymo-orchitis.
In younger, sexually active men, epididymitis is frequently caused by sexually transmitted bacteria. In older men, urinary tract infections are a more common trigger. Unlike the painless conditions above, infection-related swelling almost always comes with significant discomfort, warmth, and sometimes fever. It responds well to treatment when caught early but can lead to a secondary hydrocele if fluid accumulates during the inflammatory process.
Inguinal Hernia
An inguinal hernia occurs when tissue, usually part of the intestine, pushes through a weak spot in the abdominal wall near the groin. In men, this bulge can extend down into the scrotum and make one side appear significantly larger. The swelling tends to be more noticeable when you’re standing, coughing, or straining, and may reduce when you lie down. It often feels like a soft bulge rather than a hard lump attached to the testicle itself.
Testicular Cancer
The most common first sign of testicular cancer is a painless lump or swelling on one testicle. Most testicular lumps are not cancer, but this is the reason any new, hard, or painless lump on the testicle itself (not the softer structures around it) should be evaluated. The lump is typically firm, doesn’t move around freely, and feels like it’s part of the testicle rather than sitting on top of it.
Testicular cancer is rare overall but is the most common cancer in men between ages 15 and 35. The good news is that it has one of the highest cure rates of any cancer, even when diagnosed at advanced stages. An ultrasound can quickly distinguish a solid mass from a harmless fluid-filled cyst, which is why getting a new lump checked is straightforward and worth doing promptly.
When Sudden Pain Is an Emergency
Testicular torsion happens when a testicle twists on its spermatic cord, cutting off its blood supply. This causes sudden, severe pain and rapid swelling on one side. It is a medical emergency. Without treatment within roughly six hours, the testicle can be permanently damaged. If you experience sharp, sudden testicular pain, especially with nausea or vomiting, go to the emergency room immediately. Torsion is most common in teenagers but can occur at any age.
How to Do a Self-Check
Johns Hopkins Medicine recommends a monthly self-exam that takes about five minutes. The best time is during or right after a warm shower, when the scrotal skin is relaxed and the testicles hang lower.
- Start with one side. Gently roll the testicle between your fingers, feeling the entire surface for lumps, bumps, or hard spots.
- Locate the epididymis. You’ll feel a softer, bumpier ridge along the back and top of the testicle. This is normal anatomy, not a mass.
- Switch sides and repeat. Compare how each testicle feels. You’re establishing a baseline so you’ll notice if something changes.
A slight size difference between the two sides is normal. What you’re looking for is change: a new lump, increased firmness, or a testicle that has grown noticeably larger since last month. The U.S. Preventive Services Task Force does not recommend formal screening for testicular cancer in men without symptoms because the disease is rare and highly curable. But familiarizing yourself with what’s normal for your body means you’ll recognize something unusual if it appears.
What Gets Checked at the Doctor
If you find something that concerns you, the first step is usually a physical exam followed by a scrotal ultrasound. This painless imaging test uses sound waves to show whether a mass is solid or fluid-filled, which is the most important initial distinction. Ultrasound is highly sensitive at detecting testicular lesions, though it occasionally needs to be supplemented with additional imaging techniques to clarify whether a finding is benign or concerning. In most cases, the ultrasound provides a clear answer within minutes and can spare you weeks of unnecessary worry.