Semen is the viscous white fluid that is released when a man ejaculates. The average volume of an ejaculation is between 2.3 ml and 4.99 ml, which is from half a teaspoon to a full teaspoon. For an interspecies comparison, the average bull weighs between 1,000 and 2,000 lbs. He ejaculates between 4 ml and 8 ml, which is not much more than the average human male. Contrary to what most people believe, less than 5% of semen is made by the testicles. Ejaculations come out in squirts that have different constituents. The first squirt of each ejaculation has secretions from the Cowper (bulbourethral) glands and the Littre glands. This is precum. The prostate gland manufactures the next squirt of semen which is about 30% of the total volume of semen. On the heels of that is the relatively small but potent contribution of sperm from the testicles. The seminal vesicles hold up the rear of each ejaculation by producing up to 70% of semen. Semen has more than 300 constituents, including proteins, fats, immature sperm cells, dead parts of old sperm, and occasionally blood cells. Healthy semen tends to be mostly white and has the smell of clean, fresh bleach. Spermine from the prostate gland is what gives semen it’s bleachy smell. Semen can also smell like fresh bean sprouts, which makes sense because bean sprouts contain spermine. The reason why some men’s semen smells more bleachy than others is due to changes in the pH of semen and variations in how the body buffers it. The pH level impacts how spermine behaves. This is also why a man’s semen might smell more like bleach one day and less the next. As for why semen burns when it gets in your eyes, Spermine is a corrosive. Also, the pH of semen might cause a burning sensation in the eyes. Some women report getting a stomach ache after swallowing semen. This is usually blamed on the prostaglandins that are in semen, which might make it similar to the kind of stomach upset that some people get after taking aspirin. When people describe the way semen tastes, the words that pop up most often are “salty,” “metallic,” and, occasionally, “sweet.” As for why semen tastes salty or metallic, the amount of citrate ions stands out. These ions help semen to be a strong buffering agent, which makes it more friendly for sperm. They also create calcium citrate, which tastes salty and sour. Semen also contains magnesium, potassium, sodium, lactic acid, and zinc which contribute to a less than appealing taste. On the bright side, semen contains fructose and glucose. However, the amount of fructose and glucose can vary by as much as fourfold from man to man. One of the reasons why semen will often leave a stain when it dries on certain fabrics is because it contains a lot of protein, much of which is albumin. This is the same kind of protein that is in egg whites. As protein dries, it changes optical qualities and color. The yellowish, staining quality of semen is related to the concentration of protein in it. The sperm concentration can also have an impact. The higher the sperm count, the more opaque or yellowish the stain. The viscosity of semen is different in different men. Some men’s semen is almost as thin as water, while other guys nearly need a grease gun to squirt it out. The viscosity of semen starts to change as soon as ejaculation begins. That’s because during ejaculation, prostate-specific antigen (PSA), which is made in the prostate gland, mixes with the rest of the semen. This starts a reaction that makes semen become more watery so sperm can swim in it. Due to the liquefying power of PSA, semen becomes almost as thin as water within 5 to 20 minutes after ejaculation, regardless of how thick it may have been when it first shot out. This is why semen drips out of a woman’s vagina after intercourse. Semen gets clumpy, stringy and sticky when it’s in water, like when a guy masturbates in the bath and the semen clumps up and sticks to his skin and body hair, or when he masturbates in the shower and clumps of semen stick to hair that’s on the drain cover. When semen first comes out of the penis, it’s hydrophobic, which means it hates water. Even though it’s a liquid, when fresh semen makes contact with water, it will form clumps, like the bubbles in lava lamps. These clumps are semen’s way of protecting as much of itself as possible from water. You’ll see this occur if a guy will ejaculate into a glass of water. Everyone will be amazed. Semen used to be regarded as a vehicle for sperm and not much more, but we’re now discovering that semen has a complex relationship with a woman’s immune system. Semen starts signaling her immune system from the moment of first contact in ways that are important if pregnancy is your goal.