Cum is an informal term for semen, the fluid released from the penis during ejaculation. It can also refer to the act of reaching orgasm itself. The fluid is a complex mixture produced by several glands in the male reproductive system, and its primary biological purpose is to transport and protect sperm on their journey toward an egg.
What Semen Is Made Of
Semen is mostly water, but it contains a surprisingly complex mix of sugars, proteins, enzymes, minerals, and other compounds. It has a slightly viscous, whitish appearance, often compared to the consistency of raw egg white or runny jelly. The typical volume per ejaculation ranges from about 1.4 to 5 milliliters, roughly a quarter to a full teaspoon.
Sperm cells themselves make up only about 5 to 10% of that volume. The rest is seminal plasma, the liquid portion that keeps sperm alive and functional. A healthy ejaculate contains at least 39 million sperm total, though the concentration can vary widely from one person to another and even from one day to the next.
Where It Comes From
Semen isn’t produced in a single place. Several glands each contribute a different portion with different ingredients. The seminal vesicles, two small glands behind the bladder, produce the largest share: about 1.5 to 2 milliliters per ejaculation. Their fluid is rich in fructose (a sugar that serves as fuel for sperm) along with compounds that help the fluid clot briefly after ejaculation.
The prostate gland adds roughly 0.5 milliliters. Its contribution includes enzymes that liquefy the semen after its initial thickening, plus citric acid and other compounds that support sperm function. Two smaller glands near the base of the penis, called Cowper’s glands, contribute a small amount of clear, slippery fluid (about 0.1 milliliters) that also acts as a lubricant released before ejaculation.
The testicles produce the sperm cells themselves, which travel through a long coiled tube where they mature over about 2.5 months before being mixed into the fluid during ejaculation.
What It Does Biologically
Seminal fluid is essentially a survival kit for sperm. Each component serves a specific protective or nutritional role.
- Fuel: Fructose from the seminal vesicles gives sperm the energy they need to swim through the reproductive tract, a journey that can take hours.
- Acid protection: The vaginal environment is naturally acidic, which would quickly kill unprotected sperm. Semen is alkaline, with a pH between 7.2 and 8.0, helping to neutralize that acidity and give sperm a window of survival.
- Antioxidant defense: Seminal plasma contains antioxidant enzymes that shield sperm from oxidative damage during transit.
- Immune signaling: Components in semen interact with the lining of the uterus and cervix, triggering an immune response that, paradoxically, helps the body tolerate rather than attack the sperm. This process also appears to help prepare the uterine environment for a potential pregnancy.
Once inside the female reproductive tract, sperm can survive for up to five days. Outside the body at room temperature, they typically die within about an hour. Frozen sperm stored in a sperm bank can remain viable for decades.
Normal Appearance and Variations
Healthy semen is cloudy white or slightly gray. Its consistency can vary from thicker and gel-like to more watery depending on hydration, diet, activity level, how recently someone last ejaculated, and alcohol or drug use. Temporary dehydration, for instance, can make semen noticeably thicker in the short term. These variations are normal.
A yellowish tint is common and usually harmless. It can result from infrequent ejaculation, certain vitamins or medications, foods with dyes, or small amounts of urine mixing with the fluid in the urethra. In some cases, yellow or greenish semen can signal a urinary tract infection or a sexually transmitted infection like chlamydia or gonorrhea, particularly if accompanied by pain, burning, or unusual smell.
Pink, red, or brown semen usually means blood has mixed into the fluid, a condition called hematospermia. This sounds alarming but is often caused by something minor: a burst blood vessel, vigorous sexual activity, or mild inflammation. It can also follow a prostate biopsy or be related to prostate inflammation, high blood pressure, or, less commonly, prostate cancer. Blood that appears dark brown or black suggests older bleeding, possibly from a more significant injury. A single episode of blood in semen that resolves on its own is rarely serious, but recurring or persistent discoloration is worth getting checked.
Semen Allergy
A small number of people are genuinely allergic to proteins in seminal fluid. Estimates suggest around 40,000 women in the United States have this condition, though the real number may be higher since many people don’t report their symptoms. Reactions typically appear within minutes of contact and include itching, redness, swelling, burning, and hives on the skin that touched the semen. In more severe cases, symptoms can include swollen lips or tongue, difficulty breathing, dizziness, or nausea. Rarely, a semen allergy can trigger anaphylaxis.
One straightforward way to identify a semen allergy is to use a condom during sex. If symptoms disappear with a condom and return without one, semen is the likely cause. Doctors can confirm the diagnosis with a skin test, injecting a tiny amount of semen under the skin and watching for a reaction.