Anal masturbation is masturbation focusing on the anal area. For humans, common methods of anal masturbation include the insertion of fingers or sex toys such as butt plugs. Studies have shown that anal masturbation is common in many species.
Anal masturbation can be pleasurable for both men and women, both heterosexual and homosexual. The anus contains an abundance of erotically pleasurable nerve endings. For men, anal masturbation can be especially pleasurable because it often stimulates the prostate, which also contains an abundance of nerve endings. For women, insertion of an object into the anus can indirectly stimulate the vagina. Since the muscles of the anus contract during orgasm, the presence of an object holding the sphincter open can strengthen the sensation of the contractions and intensify orgasm for both men and women.
It is often necessary to apply lubricant to the anal area before insertion of any object, since unlike the vagina, the anus does not produce natural lubrication.
If using sex toys, it is important to remember not to insert objects with rough edges, as this can cause tears to the rectum. Inexpensive butt plugs and anal beads will sometimes have seams caused by the polymer molding process; these should be shaved or otherwise removed before use. Butt plugs, if used, should always have a flared base to prevent complete insertion. (See the wikipedia article rectal foreign body.) Anything inserted into the anus should be carefully cleaned (sterilized if possible) before and after use. Sex toys should not be shared in order to minimize STI (Sexually-transmitted infection, formerly referred to as an STD) risk.
People who have never inserted an object into the anus before may wish to begin by gently inserting a finger.¹ Afterwards, one can move up to a small butt plug. A ½" to 1" (1 to 2½ cm) diameter is generally suitable for those who have never attempted inserting objects in the anus. Objects beyond a 1½"(3½-4 cm) diameter should not be used except by those who are experienced and comfortable with it. Overstretching of the anus can cause fecal incontinence or anal fissures; see also anal stretching for a discussion. Objects should not be inserted if they cause discomfort; any blood or pain encountered is a signal to stop. Special caution is urged when inserting objects not especially designed for insertion.
¹ One should remember to defecate and lubricate the area beforehand. For those who are squeamish about potential contact with feces, a latex glove or a condom may be worn over the finger.
Men who wish to stimulate the prostate should insert a butt plug and then gently angle it toward the navel before rubbing back and forth. There are also some butt plugs specifically shaped for prostate stimulation. Recent research indicates that massage of the prostate may actually help decrease the risk of prostate cancer.
Wax candles can sometimes make inexpensive substitutes for butt plugs. One should make sure that the candles do not contain lead. Like any object inserted in the anus, the candle should not be inserted more than eight inches or beyond one's comfort level - to do so can cause tears to the sigmoid colon. Candles are also more rigid, and therefore when using a candle one should exercise special care to avoid injury. It is also important to remember not to completely insert the candle, since unlike butt plugs, candles do not have flared bases.
Small hard boiled eggs (without shells) can usually be safely inserted in the rectum and defecated as feces. Hard boiling an egg can raise its internal temperature to a dangerous level, so the egg should be cooled before use. Placing the egg in a refrigerator will generally cool the egg down quickly and to an acceptable temperature. Since 1 to 1½ inches (3 to 4 cm) is generally the largest diameter that is safe and comfortable for the general population, the eggs found in supermarket dairy cases may be too large. Seek "medium" or "small" sized eggs if possible. Remember to lubricate the eggs and the anal area before insertion. Again, it is important to exercise common sense and not to insert objects larger than one's comfort level.
Stories (or urban legends) have sometimes circulated regarding the insertion of gerbils or light bulbs. The insertion of these objects is not safe. Besides being too large in diameter and virtually impossible to retrieve if completely inserted, a light bulb could have medically catastrophic consequences if it were to shatter while inside the rectum.
The purpose of the anus is to remove feces from the body; therefore when inserting objects into the anus one may encounter feces. This can make cleanup especially important and difficult. One may wish to cover butt plugs or other objects with a condom before insertion and then dispose of afterwards to simplify the cleaning process.
Minimizing the amount of faeces present in the rectum may also help. To do this, one may try increasing the amount of insoluble fibre present in one's food. Besides being beneficial for general health, insoluble fibre will also help clear the rectum of faeces when defecating.