Hydrocele in adults develops when fluid builds up between the layers of tissue surrounding a testicle, called the tunica vaginalis. This tissue naturally secretes small amounts of fluid, which is normally reabsorbed through nearby veins and lymphatic vessels in the spermatic cord. A hydrocele forms when that balance tips: either the tissue produces more fluid than usual, or the body’s ability to drain it slows down. Several specific conditions can trigger that imbalance.
How Fluid Normally Moves Around the Testicle
The tunica vaginalis is a thin, two-layered membrane that wraps around each testicle. It constantly secretes a small amount of lubricating fluid, similar to how other membranes in the body keep organs from sticking to surrounding tissue. Under normal conditions, veins and lymphatic vessels running through the spermatic cord steadily absorb this fluid, keeping the volume so low you’d never notice it.
When something disrupts either side of that equation, fluid accumulates. The swelling is typically painless, feels soft, and doesn’t go away when you lie down. It also can’t be pushed back into the abdomen, which helps distinguish it from a hernia. In adults, the hydrocele sac is usually “noncommunicating,” meaning there’s no open channel between the scrotum and the abdominal cavity. The problem is local: something near the testicle is producing too much fluid or blocking drainage.
Infection and Inflammation
The most common identifiable trigger for adult hydrocele in developed countries is an infection or inflammation involving the testicle or the coiled tube behind it (the epididymis). Epididymitis, often caused by bacterial infection, leads to what’s called a reactive hydrocele. The inflamed tissue ramps up fluid production, and the surrounding structures can’t absorb it fast enough. Orchitis (inflammation of the testicle itself) works through the same mechanism.
These infections are frequently linked to sexually transmitted bacteria in younger men and urinary tract bacteria in older men. The hydrocele that forms alongside the infection may shrink once the underlying infection clears, but in some cases the fluid persists long after the inflammation has resolved.
Parasitic Infection (Lymphatic Filariasis)
Globally, the single largest cause of hydrocele is lymphatic filariasis, a parasitic disease spread by mosquitoes in tropical and subtropical regions. The World Health Organization estimates that 25 million men worldwide have a hydrocele caused by this infection. Microscopic roundworms lodge inside the lymphatic vessels, physically blocking the drainage pathways that would normally reabsorb scrotal fluid. Over time, this obstruction can produce massive, chronic swelling.
The disease is most prevalent in parts of sub-Saharan Africa, South Asia, and the Pacific Islands. In these regions, hydrocele is one of the hallmark chronic complications of filariasis, alongside severe limb swelling. At least 36 million people globally live with chronic complications from the infection.
Scrotal Trauma and Surgery
A direct injury to the scrotum can disrupt the delicate balance between fluid production and absorption within the tunica. The trauma triggers local inflammation, which increases fluid output, and may also damage the small lymphatic and venous channels responsible for drainage. A hydrocele that follows an injury may appear days to weeks later as the inflammatory response plays out.
Surgery in the scrotal or inguinal area, including hernia repair or varicocele correction, can also lead to hydrocele formation. The mechanism is similar: surgical disruption of lymphatic drainage pathways or local tissue irritation shifts the fluid balance. Post-surgical hydroceles are a well-recognized complication and sometimes resolve on their own over several months, though not always.
Systemic Conditions That Cause Fluid Overload
Conditions that affect the body’s overall fluid balance can contribute to scrotal swelling, including hydrocele. Heart failure, severe liver disease (cirrhosis), and kidney disorders all cause the body to retain excess fluid. When that generalized fluid overload reaches the scrotal tissues, it can overwhelm local absorption capacity. In these cases, the hydrocele is a symptom of a broader problem rather than a standalone condition, and treating the underlying disease is more important than addressing the scrotal fluid itself.
Idiopathic Hydrocele: No Clear Cause
In many adult men, no specific trigger is ever identified. These are called idiopathic hydroceles, and they’re actually the most common type seen in clinical practice in high-income countries. They tend to develop gradually, often in men over 40, and grow slowly enough that months or years may pass before the swelling becomes noticeable or bothersome. The underlying mechanism is still the same imbalance between secretion and reabsorption, but what initiates it remains unclear. Age-related changes in lymphatic drainage efficiency are one likely contributor.
How Hydroceles Are Treated
Small, painless hydroceles that aren’t growing often don’t need treatment at all. When the swelling becomes uncomfortable, cosmetically bothersome, or large enough to interfere with daily life, two main options exist.
Surgical removal (hydrocelectomy) has the highest cure rate, approaching 100% in clinical trials. Recovery typically involves a few weeks of restricted activity and some post-operative discomfort. The trade-off is a higher complication rate compared to less invasive options: studies report overall complication rates of 16 to 19%, with post-operative infection occurring in roughly 1 in 10 cases.
Aspiration and sclerotherapy is a less invasive alternative. A needle drains the fluid, and an irritant solution is injected to encourage the tissue layers to seal together. Initial resolution rates sit around 59%, climbing to roughly 68% after a second procedure and 73% after a third. When hydroceles do recur after sclerotherapy, they tend to come back fairly quickly, with a median recurrence time of about 44 days. The major advantage is a substantially lower complication rate (around 3.4%), shorter recovery, and less long-term pain. A randomized trial comparing sclerotherapy to surgery found no statistically significant difference in ultimate cure rates, making sclerotherapy a reasonable first step for men who want to avoid surgery.
For hydroceles caused by an underlying condition, such as infection or heart failure, treating the root cause is the priority. The fluid may resolve on its own once the underlying issue is managed.