Pre-ejaculate (also known as pre-ejaculatory fluid, preseminal fluid, or Cowper's fluid, and colloquially as pre-cum) is the clear, colorless, viscous fluid that emits from the urethra of a man's penis when he is sexually aroused. It is similar in composition to semen, but has some significant chemical differences. Among men with certain infectious diseases, pre-ejaculate can often contain disease pathogens. The presence of sperm in the fluid appears to be rare. Pre-ejaculate is believed to function as a lubricant and an acid neutralizer. The amount of pre-ejaculate emitted varies widely between individual men.
Origin and composition
The fluid is discharged during arousal, masturbation, foreplay or at an early stage during sex, some time before the man fully reaches orgasm and semen is ejaculated. It is primarily produced by the bulbourethral glands (Cowper's glands), with the glands of Littre (the mucus-secreting urethral glands) also contributing.
The amount of fluid that the human male issues varies widely among individuals. Some men do not produce any pre-ejaculate fluid, while others emit as much as 5 ml.
Pre-ejaculate contains some chemicals associated with semen, such as acid phosphatase. Some semen markers, such as gamma-glutamyltransferase, are completely absent from pre-ejaculate fluid.
Acidic environments are hostile to sperm. Pre-ejaculate neutralizes residual acidity in the urethra caused by urine, creating a more favorable environment for the passage of sperm. The vagina is normally acidic, so the deposit of pre-ejaculate before the emission of semen may change the vaginal environment to promote sperm survival.
Pre-ejaculate also acts as a lubricant during sexual activity, and plays a role in semen coagulation. Men who do not produce any noticeable amount of pre-ejaculate past that used to lubricate the urethra are often benefited by actively exercising the pubococcygeus muscle, releasing a small amount of semen and seminal fluid before the orgasm occurs in full. These fluids function as well as the pre-seminal fluids at neutralizing acid and as lubricants.
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