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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. The presence of sperm in the fluid is debated. Research has found no or low levels of sperm in pre-ejaculate, though these existing studies are non-generalizable due to examining small numbers of men. A contrary, yet non-generalizable study that found mixed evidence, including individual cases of a high sperm concentration, has been recently published. Pre-ejaculate is believed to function as a lubricant and an acid neutralizer. The amount of pre-ejaculate emitted varies widely between individual men. There are some cases where men do not pre-ejaculate.
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.
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 seminal fluid before the orgasm occurs in full.
Popular belief--dating back to a 1966 Masters & Johnson study --states that pre-ejaculate may contain sperm that can cause pregnancy, which is a common basis of argument against the use of coitus interruptus (withdrawal) as a contraceptive method. However, some studies have found that withdrawal could be almost as effective as condoms in preventing pregnancy. There have been several small-scale studies (sample sizes ranging from 4 to 23) that conclude no sperm is present, and thus, pre-ejaculate is ineffectual at causing pregnancy.
A noted limitation to these previous studies' findings is that pre-ejaculate samples were analyzed after the critical two-minute point. That is, looking for motile sperm in small amounts of pre-ejaculate via microscope after two minutes--when the sample has most likely dried--makes examination and evaluation "extremely difficult." Thus, in March 2011 a team of researchers assembled 27 male volunteers and analyzed their pre-ejaculate samples within two minutes after producing them. The researchers found that 11 of the 27 men (41%) produced pre-ejaculatory samples that contained sperm, and 10 of these samples (37%) contained a "fair amount" of motile sperm (i.e. as little as 1 million to as many as 35 million). As a point of reference, a study showed that, of couples who conceived within a year of trying, only 2.5% included a male partner with a total sperm count (per ejaculate) of 23 million sperm or less. However, across a wide range of observed values, total sperm count (as with other identified semen and sperm characteristics) has weak power to predict which couples are at risk of pregnancy.
It is widely believed that urinating after an ejaculation will flush the urethra of remaining sperm. Therefore, some of the subjects in the March 2011 study who produced sperm in their pre-ejaculate did urinate (sometimes more than once) before producing their sample. However, two things need to be kept in mind. First, the study suggests that some men can leak sperm into their pre-ejaculate (though the authors do not extrapolate on this supposition and the possible causes of such a phenomenon). Second, and most importantly, the authors admit that some of their subjects who submitted sperm-positive pre-ejaculate samples could have actually used their ejaculate--due to failure of producing pre-ejaculate--to avoid the "embarrassment" of not producing pre-ejaculate.
In rare cases, a man may produce an excessive amount of pre-ejaculate fluid that can be a cause of embarrassment or irritation. A few case reports have indicated satisfactory results when such men are treated with a 5-alpha-reductase inhibitor.
In Islam, after the emission of pre-ejaculate fluid, ritual purification is recommended, by washing the affected areas (including clothing) with water. The pre-ejaculate fluid calls for washing and ablution before praying. However, it does not require ritual purificatory bath, unlike the semen which comes after the ejaculation.