The scrotum’s primary job is temperature control. It keeps the testes about 2 to 3°C cooler than the rest of the body, which is the narrow range sperm production requires. Even a 1.5 to 2°C increase in scrotal temperature can shut down sperm production. Beyond temperature regulation, the scrotum also provides a physical barrier between the testes and the outside world, and it houses the blood vessels and nerves that supply each testicle.
Temperature Regulation Is the Main Function
Sperm cells are surprisingly fragile when it comes to heat. They can only be produced reliably at temperatures a few degrees below the body’s core of about 37°C. That’s the entire reason the testes sit outside the abdominal cavity in the first place. The scrotum makes this possible by acting as a kind of biological thermostat, constantly adjusting how close or far the testes hang from the body.
Two separate muscles do the heavy lifting here. The dartos is a thin sheet of smooth muscle embedded in the scrotal wall itself. When it’s cold, the dartos contracts, wrinkling the scrotal skin and pulling it tight against the body to conserve heat. When it’s warm, the dartos relaxes, letting the scrotum hang lower and increasing the surface area exposed to air. This muscle responds automatically through the sympathetic nervous system, meaning you have no conscious control over it.
The cremaster muscle works alongside the dartos but operates independently. It’s a striated muscle connected to the abdominal wall that can physically lift or lower each testicle inside the scrotum. In cold conditions, the cremaster contracts and draws the testes closer to the warm body core. In warm conditions, it relaxes so the testes drop farther away. The cremaster also contracts in response to touch or perceived threat, which is why a light stroke on the inner thigh causes the testicle on that side to rise. This is called the cremasteric reflex, and doctors sometimes test it when evaluating scrotal pain.
Sweat glands in the scrotal skin add a third cooling mechanism. The scrotum has a higher density of sweat glands than most skin on the body, allowing evaporative cooling when ambient temperatures climb above what muscle adjustments alone can handle.
How the Scrotum Is Built
The scrotum looks simple from the outside, but it’s actually made of six distinct layers stacked from the skin inward. The outermost layer is thin, pigmented skin. Just beneath that sits the dartos fascia, which contains the smooth muscle responsible for scrotal wrinkling. Deeper layers include connective tissue sheaths derived from the abdominal wall muscles, each one a remnant of the path the testes followed when they descended during fetal development. The innermost layer, the tunica vaginalis, is a thin membrane that wraps around each testicle and provides a small amount of lubricating fluid so the testes can move freely within the sac.
A vertical wall of tissue called the scrotal septum divides the scrotum into two separate compartments, one for each testicle. This means each testis has its own independent set of layers and its own blood supply, so a problem on one side doesn’t necessarily affect the other.
Physical Protection
The scrotum offers some protection to the testes, but it’s limited. There are no bones or thick muscle layers shielding the area the way the ribcage protects the heart and lungs. The scrotal skin and its underlying layers absorb minor bumps, and the cremasteric reflex can pull the testes upward and out of harm’s way in response to sudden stimuli. Most of the time, the testes can absorb the shock of a mild impact without lasting damage, but the scrotum is not built to withstand forceful blows.
How the Testes Get There
During fetal development, the testes form inside the abdomen near the kidneys. Between 28 and 40 weeks of gestation, they migrate downward through the inguinal canal and into the scrotum. This journey is what creates the layered structure of the scrotal wall, since each tissue the testes pass through on their way down contributes a layer that follows them into the sac.
In about 3 to 4% of full-term male newborns, one or both testes haven’t completed this descent by birth. The condition is more common in premature infants, since the descent window extends to 40 weeks. In most cases, the testes finish dropping on their own within the first few months of life. When they don’t, the concern is exactly what the scrotum is designed to address: a testicle stuck at body temperature inside the abdomen can’t produce sperm normally and may face other long-term complications.
What the Cremasteric Reflex Reveals
The cremasteric reflex, that involuntary pulling-up of the testicle when the inner thigh is stroked, runs through nerves originating from the L1 and L2 spinal levels. Sensory fibers detect the touch on the thigh, send a signal to the spinal cord, and motor fibers fire back to contract the cremaster muscle on the same side.
This reflex has clinical value because it tends to disappear when the spermatic cord twists, a condition called testicular torsion. Torsion cuts off blood flow to the testicle and requires emergency treatment. Studies have found the cremasteric reflex absent in nearly all confirmed torsion cases, making it one of the first things checked during an evaluation of sudden, severe scrotal pain. That said, some healthy males naturally lack the reflex, so its absence alone isn’t enough to confirm a diagnosis.