Semen (pronounced SEE-men or SEE-mən) is the fluid that comes out from the end of a man's penis when he has an orgasm (the height of sexual excitement) and ejaculates. It is usually a white or yellowish, sticky substance made up of sperm (male cells for sexual reproduction) floating in a fluid called seminal plasma that has water and different chemicals in it. Normally, an ejaculation makes between 1.5 and 5 millilitres (up to one teaspoonful) of semen.

Some scientists think that semen that is taken into a woman's body causes her not to feel depressed or sad. On the other hand, if semen touches another person's body, it can pass on sexually transmitted infections (STIs). In a few cases, it can also make the other person's immune system weaker, or cause the person to have an allergic reaction. The risks of these health problems happening can be reduced if the man wears a condom when having sex.

Many cultures around the world once thought or still think that semen has special or even magical qualities. Showing semen in forms of popular culture such as art and movies has for a long time been taboo, that is, not generally accepted by society. However, since the late 20th century, artists and moviemakers have done so more often.

The English word semen comes from the Latin word sēmen, which means "seed".[1] In fact, seed was an old-fashioned name for semen.[2] The Latin word sēmen itself came from another Latin word, serěre, which means "to plant (a plant into the ground) or to sow (seeds in the earth)".[1] It was once thought that semen was like a seed that grew into a baby after being "planted" inside a woman's body.

Another name for semen is ejaculate. Some slang words for semen are cream, cum, jism, jizz, jazz load, spooge, spunk, nut, or wad.[original research?]

Semen is the fluid that comes out from the end of a man's penis when he has an orgasm (the height of sexual excitement) and ejaculates. It is usually white, but may also be slightly grey or yellow.[3] If there is blood in the semen, it can look pink or reddish. This is a condition called hematospermia, and may be because of some blockage, inflammation, infection or injury to some part of the male sex organs, such as the urethra, epididymis, prostate or testicles. A doctor should be seen if the pink or reddish colour does not go away after a few days.[4]

Men ejaculate different amounts of semen. Normally, an ejaculation makes between 1.5 and 5 millilitres (up to one teaspoonful) of semen.[5] More semen usually comes out if a man has not ejaculated for many days, or if he has been stimulated (made sexually excited) for a long time. Older men make less semen. If a man ejaculates an unusually small amount of semen, this is a medical condition called hypospermia.

After a man has ejaculated, semen first becomes slightly thick and sticky, and may feel a bit like jelly and clump together in globs. Scientists think that semen does this so that if the man has had sex with a woman and has ejaculated inside her vagina, the semen stays in her vagina for longer and does not leak out. Between five and 40 minutes after this, semen becomes more liquid and watery. This probably allows the sperm in the semen to move through the vagina and into the woman's uterus and Fallopian tubes to try and fertilize an ovum (egg cell). If semen is ejaculated outside the body, after becoming watery it eventually dries up.[3]

Semen is made up of sperm (male cells for sexual reproduction) floating in a fluid called seminal plasma. Sperm, also called spermatozoa, are made by a man's testicles and mature (grow up) in the epididymis. The fluids in seminal plasma come from different glands in the man's body: the seminal vesicles, prostate and bulbourethral glands (also called the Cowper's glands). (Glands are special organs in the body that make chemicals.) The table below shows the substances that make up semen and the glands that produce them:[3]

Seminal plasma protects and provides food for sperm as they travel inside a woman's body. The inside of a woman'a vagina does not suit sperm cells as it is acidic. To protect the sperm from the acid, seminal plasma is alkaline. A woman's immune system also tries to kill organisms (living things) that are not part of her body. Seminal plasma has chemicals called prostaglandins in it to stop the woman's body from killing the sperm.

Semen that does not have any germs in it (see below) is not harmful if it is swallowed, for example after a person has had oral sex with a man and the man ejaculates in that person's mouth.

Semen quality refers to how well the sperm in a man's semen can fertilize a woman's ova. The better a man's semen quality is, the better chances he has to make a woman pregnant. A 1992 World Health Organization book said that an ejaculation of normal human semen has:[6]

The number of sperm in an ejaculation of semen depends on many things. There may be more sperm if:

If there are an unusually low number of sperm in an ejaculation, this is called oligospermia. If there are no sperm at all, this is called azoospermia. A man with oligospermia or azoospermia is usually infertile, and cannot or finds it very hard to make a woman pregnant by having sex with her.

If the semen does not have infections, it is okay to swallow semen. A woman cannot get pregnant from swallowing semen in her mouth. It is okay if a man swallows his own semen. Two doctors say it is good if a woman swallows semen often. They say women get breast cancer less if they swallow semen.[7] The doctors don't know why. Other doctors must do more tests.

Studies seem to say that semen is an anti-depressant. This means that it causes women not to feel depressed or sad. The studies found that when men had sex with women without using condoms, and the men's semen was taken into the women's vaginas, the women had better moods and felt happier. Scientists do not yet know if the same thing happens when semen is swallowed after oral sex, but some of them think it may.[8]

If a man has a sexually transmitted infection or STI (an infection that is passed from one person to another by sex), the germs that cause the disease can appear in his semen. If the person that the man has sex with touches the semen, he or she can become infected by the germs and pick up the disease. HIV, chlamydia, gonorrhea, hepatitis B, herpes and syphillis are examples of STIs. One of the ways for a man to lower the chance of passing on an STI to his sexual partner is to wear a condom on his penis when having sex. Getting semen in the mouth can be bad if the penis or semen has infections.

If semen gets in the eye, the eye will hurt. Wash the eye with warm water. Wash the eye for a few minutes. Some doctors say to get tested for infections.[9]

Some scientists think that parts of semen, such as sperm and seminal plasma, can make another person's immune system weaker. Experiments show that when substances in a man's semen enter another person's body, that person's body makes antibodies. Antibodies are large Y-shaped proteins used by the body's immune system to stop foreign objects from harming the body. However, the antibodies made in response to substances in semen attack one of the body's own cells, called T lymphocytes.[10] This weakens the body's immune system.

In a very small number of cases, people have experienced allergic reactions when they touched semen. This is called human seminal plasma hypersensitivity. The symptoms (signs of the medical problem) can either be near the part of the body which touched the semen, or all over the body. They may include itching of the vagina, redness, swelling or blisters within 30 minutes of contact. They may also include itching and hives (large, red, itchy patches) all over the body, and even difficulty breathing.[11]

The best way to test for human seminal plasma hypersensitivity is for a man to use a condom when having sex. When a condom is used, after ejaculation the man's semen stays inside the condom and does not touch the body of the person he is having sex with. If the man's sexual partner usually has allergic symptoms to semen but does not have any when a condom is used, this may show that his partner's body is extra-sensitive to semen. A person can often get over a mild semen allergy by coming into contact with semen often.[12] If the allergic reaction is very bad, the person should see a doctor, especially if she is a woman trying to get pregnant. In such cases, it may be necessary for the woman to have a baby through artificial insemination. This is a medical way of fertilizing a woman's ova using a man's sperm without the man and the woman having sexual intercourse.

Many cultures around the world once thought or still think that semen has special or even magical qualities. Some examples are set out below:

Displaying semen in forms of popular culture such as art and movies has for a long time been taboo, that is, not generally accepted by society. However, since the late 20th century artists and moviemakers have done so more often.

The American photographer Andres Serrano sometimes takes photographs of body fluids and displays them as artworks. One example is Blood and Semen II (1990), which is a picture of blood and semen mixed together. Some people are shocked by such pictures and think it is wrong of him to make them, while others think that as an artist he is free to create such works.[19] Another of Serrano's pictures, Blood and Semen III, was featured on the cover of the 1996 music album Load by the American heavy metal band Metallica.[20]

The United Kingdom-based artists Gilbert Proesch and George Passmore, better known as Gilbert and George, have also used semen and other body fluids to create artworks.[21]

Apart from pornographic movies showing people having sex, semen is usually not shown in movies as many people think that doing so is obscene (not decent). However, some movies that have shown semen are the American comedy movies There's Something about Mary (1998),[22] American Pie (1999),[23] Scary Movie (2000)[24] and Scary Movie 2 (2001).[25] In the Spanish movie Y tu mamá también (And Your Mother Too, 2001), there is a scene where two high-school boys who are friends lie on diving boards over a swimming pool and masturbate (make themselves sexually excited). Semen is later shown floating on the water.[26] Such movies are usually not thought to be suitable for children to watch.