The scrotum is a pouch of skin and muscle that hangs below the penis and holds the testicles. Its primary job is keeping the testicles at the right temperature for producing sperm, which requires conditions 2 to 3 degrees Celsius (about 4 to 5 degrees Fahrenheit) cooler than the rest of the body. It also physically protects the testicles from impact and compression.
What the Scrotum Is Made Of
The scrotum looks simple from the outside, but it’s built from multiple layers that mirror the layers of the abdominal wall. From the surface inward, those layers are: skin, a thin muscular layer called the dartos, a connective tissue covering, the cremaster muscle, another layer of connective tissue, and finally a smooth membrane that wraps each testicle individually.
Two of those layers are muscles, and both play active roles. The dartos is a thin sheet of muscle woven into the scrotal skin itself. When it contracts, the scrotum tightens and becomes wrinkled, pulling the testicles closer to the body. The cremaster muscle runs along the spermatic cord (the cord-like structure connecting each testicle to the rest of the body) and can lift or lower each testicle independently.
A wall of tissue called the scrotal septum divides the scrotum into two compartments, one for each testicle. The left testicle typically hangs slightly lower than the right, which is normal and helps prevent the two from compressing each other.
How It Regulates Temperature
Sperm production is extremely sensitive to heat. An increase of just 1.5 to 2 degrees Celsius in testicular temperature can shut down sperm production. The scrotum solves this problem by housing the testicles outside the body’s core, creating a temperature gradient that keeps them within a functional range.
This isn’t a passive process. The scrotum actively adjusts. In cold conditions, the dartos and cremaster muscles contract, drawing the testicles upward toward the warmth of the body and reducing the surface area of exposed skin. In warm conditions, both muscles relax, allowing the scrotum to hang lower and loose so heat can dissipate more effectively. You can see this happening in real time: the scrotum looks tighter and smaller after a cold shower and hangs more loosely on a hot day.
A network of veins called the pampiniform plexus also helps. These veins wrap around the artery that supplies blood to each testicle, cooling the incoming arterial blood before it reaches the organ. It works like a heat exchanger, ensuring warm blood from the body doesn’t raise testicular temperature.
The Cremasteric Reflex
If you stroke the inner thigh, the testicle on that same side will reflexively pull upward. This is the cremasteric reflex, driven by a nerve pathway that originates from the lower spine. The sensory signal from the thigh travels to the spinal cord, which sends a motor signal back to the cremaster muscle, causing it to contract and retract the testicle toward the groin.
This reflex serves a protective function, pulling the testicles out of harm’s way in response to nearby stimulation. It also contributes to temperature regulation. Doctors sometimes test it when evaluating sudden scrotal pain, because an absent cremasteric reflex can be a sign of testicular torsion, a condition where the testicle twists on its cord and loses blood supply. That said, the reflex is naturally absent in a significant percentage of boys, so a missing reflex alone doesn’t confirm a problem.
How the Scrotum Develops
During fetal development, the testicles don’t start in the scrotum. They form deep inside the abdomen, near the kidneys, and gradually descend in two stages. The first stage moves them from the back of the abdomen down to the groin area by around the eighth week of pregnancy. The second stage, which depends on male hormones, moves them from the groin through the inguinal canal and into the scrotum, beginning around the 26th week. In most cases, both testicles are fully in the scrotum by the 33rd week of pregnancy.
Sometimes one or both testicles don’t complete this journey, a condition called cryptorchidism (undescended testicle). This is the most common genital condition found in newborn boys. It matters because a testicle that stays inside the body is exposed to core body temperature, which damages the cells responsible for sperm production and increases the risk of testicular cancer later in life. Most undescended testicles will drop on their own within the first few months after birth, but those that don’t are typically corrected with a minor surgical procedure during infancy.
Common Conditions That Affect the Scrotum
Several conditions can cause scrotal swelling, pain, or changes in appearance. The most common include:
- Varicocele: Enlarged veins within the scrotum, similar to varicose veins in the legs. Blood pools in the veins instead of circulating efficiently. Varicoceles usually develop during puberty, almost always appear on the left side, and often cause no symptoms at all. When they do, the typical complaint is a dull, aching discomfort that worsens with standing and improves when lying down. They can sometimes affect sperm production and are one of the more treatable causes of male infertility.
- Hydrocele: A buildup of fluid around a testicle that causes painless swelling. Hydroceles are common in newborns and usually resolve on their own. In adults, they can develop after injury or infection.
- Spermatocele: A fluid-filled cyst that forms near the top of a testicle. These are almost always painless, benign, and discovered by accident during a physical exam or self-check.
- Testicular torsion: A medical emergency where a testicle rotates on its spermatic cord, cutting off blood supply. This causes sudden, severe pain and swelling. It most commonly affects adolescents and requires surgery within hours to save the testicle.
Scrotal Skin and Sensitivity
Scrotal skin is thinner than skin on most other parts of the body, which is part of what makes it effective at releasing heat. It’s also more pigmented than surrounding skin, contains many sweat glands, and has a rich nerve supply that makes it highly sensitive to touch, temperature, and pain. Hair follicles on the scrotum become active during puberty.
Because the skin is thin and exposed, it’s susceptible to irritation from friction, moisture, and fungal infections. Keeping the area clean and dry helps prevent common issues like jock itch. The scrotum’s sensitivity to temperature changes also means it responds noticeably to everyday situations like exercise, hot baths, or sitting for long periods, all of which are normal variations in how the scrotum looks and feels throughout the day.