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(also known as pre-ejaculatory fluid or Cowper's fluid) is the clear lubricating fluid that is issued from a man's penis when he is aroused. Slang terms for pre-ejaculate include pre-come, pre-cum, dog water, and speed drop.
The fluid is usually secreted by Cowper's glands during foreplay or at an early stage during sex, some time before the man reaches orgasm and semen is ejaculated. Pre-ejaculatory fluid prepares the urethra for the passage of semen and neutralizes acidity due to any residual urine. It also lubricates the movement of the foreskin over the glans. The amount of fluid that the human male can issue varies widely between individuals, from imperceptible amounts to a copious flow.
A problem for couples who seek to avoid pregnancy, however, is that the pre-ejaculate may contain sperm. This is one additional reason why withdrawal (coitus interruptus) is not considered to be a reliable method of birth control. There have been no large-
scale studies of sperm in pre-ejaculate, but some smaller-
scale studies suggest that any sperm present may be ineffectual at causing pregnancy.[1] It is commonly held, but as yet unverified, that pre-ejaculate may pick up existing sperm in the urethra if the man has not urinated since his last ejaculation.
An article in the April 2003 edition of the Journal of Assisted Reproduction & Genetics set out to determine "if spermatozoa are present in the preejaculatory penile secretion, originating from Cowper's gland." After seeing that none of the pre-ejaculate contained sperm, they concluded that "Preejaculatory fluid secreted at the tip of the urethra from Cowper's gland during sexual stimulation did not contain sperm and therefore cannot be responsible for pregnancies during coitus interruptus" [2]
A more serious problem is those same studies have shown the presence of HIV, the virus responsible for the disease AIDS, in pre-ejaculate. Although the frequency of HIV transmission through oral-genital contact is fairly low [3] a risk still exists. Pre-ejaculate can also transmit other STDs.