How HIV Is Transmitted

HIV is transferred when blood, semen, pre-ejaculate fluid (pre-come), cervical fluids, vaginal fluids or breast milk come into contact with a person’s mucus membranes or blood system.  Saliva, sweat, tears, feces and urine do not transmit the virus (although who really wants to be playing with feces or urine anyway…icky, but that does partially explain why you can’t get it from a toilet seat).

What this means is it’s usually only transferred through sex or sharing needles, although a mother may pass the virus to her baby during birth or breast feeding, and in EXTREMELY RARE cases, a person may get it from receiving a blood transfusion.  Having said that, here are more details on the why and how it’s transmitted:

Sharing Needles

Anal Sex/Vaginal Sex

Oral Sex


Mutual Masturbation/Foreplay

Other Factors That Determine Sexual Risk


Ways You Definitely Can’t Get It

What Is Risk?


Sharing Needles

I’ve never used intravenous drugs myself, but if you do happen to use them, please be aware that in addition to the damage the drug does to your body, if you share needles, you may also acquire HIV.  If you’re going to do these drugs, don’t share your needles, or if you do, clean them out properly between each person.  Although the virus will die off eventually inside a needle, it lives much longer in a needle than it does in the open air.

Health workers will sometimes become infected by accidental needle sticks (i.e. they stick a needle into an infected person then accidentally stick themselves).  But, if you’re a health care worker, I would hope you already know everything you need to know about this.


Anal Sex/Vaginal Intercourse (AKA Fucking)

Unprotected fucking is the most dangerous sexual practice for HIV transmission.  Most cases of HIV transmission are due to these activities.  Anal sex is slightly more dangerous than vaginal sex.  This includes anal sex on a woman too!  These activities are dangerous for both partners, although the person receiving is at a higher risk than the person giving.  Remember, guys, the urethra (your piss-hole) is a mucus membrane.   Infected fluids can come into contact with a mucus membrane or cut and enter the body.  Anal sex is considered the most dangerous because the rectum’s lining is a very fragile thing.  During anal sex, it is very easy to tear that lining, providing an easy route for HIV to enter.  The danger for the person giving is based on tearing that lining as well, thus causing the presence of blood.  If the infected blood comes into contact with a cut (even very small cuts that aren’t visible to the naked eye) or the urethra, transmission can occur.  The risk with vaginal sex not only includes the possibility of cuts to the lining of the vagina, but vaginal fluids and cervical fluids also contain the virus.


Oral Sex

Next, although SIGNIFICANTLY lower in the risk area, is unprotected oral sex.  The risk, however, is almost entirely on the person giving, not receiving, oral sex.  The mouth has mucus membranes, although less fragile than the urethra, vagina or anus.  So, if pre-come, vaginal fluids or semen get in your mouth, you may get infected.  This is especially true if you have cuts or sores in your mouth.  Saliva does offer some protection, but just some.  Saliva has a property that inhibits infection of HIV, but if enough fluids get in the right place, there’s nothing saliva can do.  Pre-come does contain the virus, but not in as large a quantity as semen.  So, if he doesn’t come in your mouth, and you don’t have cuts or sores in your mouth, you’ll probably, but not definitely, be okay.  Vaginal fluids have a concentration of the virus somewhere between pre-come and semen.  There have been documented cases of people getting HIV from giving oral sex to men, but those are not very common, and almost always include the guy coming in the person’s mouth.  There have also been documented cases of people getting HIV from performing oral sex on a woman, but those are even less common. 

For the person receiving oral sex, if the person giving the oral sex doesn’t have VISIBLE blood in his or her mouth, you are okay.  In the over twenty years since we discovered this disease, there has never been a documented case of someone getting it from receiving oral sex, but that doesn’t necessarily mean it doesn’t happen, just that it’s very, very unlikely.  The Center for Disease Control (CDC) does state that there is a “theoretical” possibility that a person could transmit the virus this way, if the saliva is contaminated with blood.  They use the term theoretical because they have yet to have a documented case of it being transmitted this way.  Let’s think about that for a moment too, if people could get it that way, don’t you think at least one person would have stepped forward and said so by now?  Keep in mind though, other Sexually Transmitted Diseases (STDs) may be passed through both giving and receiving oral sex.

There have been numerous studies on the risks of oral sex; however, two recent ones seem the most conclusive, although they came up with different conclusions and looked at the risks from different angles.  The first was a study of people who were recently diagnosed as being HIV positive.  This study found that about 6% to 7% of the newly infected individuals got it from performing oral sex on a man.  In these cases, half of them had severe gum problems and all but one of them swallowed semen.  The one that didn’t swallow semen also contracted gonorrhea, so it is believe that made him more susceptible to HIV infection.  This is a startling study, but needs to be kept in the perspective that it was a rather small sampling (about 125 people total), and those numbers may have been a fluke.  The other study followed about 200 gay men who started the study as HIV negative, and only performed oral sex on men during the study period.  In this study, only one man tested positive, and it is believed he contracted the disease via anal sex prior to the study beginning.  Of those men, few of them used condoms for oral sex, most swallowed semen, and a good number reported performing oral sex on a man they knew to be HIV positive.  So, the findings of that study state that the risk of oral sex is somewhere between 0% to 2%.  When you look at all the studies combined, it seems the number of people who get the virus via oral sex ranges somewhere between 1% to 5% of all sexually transmitted HIV cases.  So the numbers are very low, but do point to the fact that the risk is there.  It is, however, difficult for them to really get an estimate of oral sex transmission because of the fact that many people do not only participate in oral sex and usually also have anal and/or vaginal sex.



Rimming, graphically, means licking/sucking someone’s asshole.  This is considered a relatively safe activity as far as HIV goes, but you can get different STDs or other infections through this behavior.


Mutual Masturbation/Foreplay

Mutual masturbation, deep kissing (French kissing), frottage (rubbing against each other without insertion),  and licking any body other than the genitals are considered safe (AKA no risk of transmission at all).  There has only been one documented case of transmission through deep kissing, and in that case, both people had severe bleeding gums…which is kind of icky in and of itself.  Mutual masturbation is perfectly safe as long as you don’t have fresh, bleeding cuts on your hand, and even then, the risk is small.  It is advisable, though, not to take your hand with the other person’s fluids on it and place it into a risky place, but if you happen to do that, the risk is still small.  If you play with sex toys, use caution.  Although the virus dies very quickly when exposed to air, if not enough time passes, and you share a toy, transmission could occur, although the risk is very low.  Breast milk is only really dangerous in larger quantities, such as baby feeding, and not when accidentally encountered during sex.


Other Factors That Determine Sexual Risk

A point to mention when talking about risk is that whether a guy is circumcised or not will impact his risk of becoming infected.  Circumcision is a process where the foreskin of the penis is cut off, usually shortly after birth.  Uncircumcised men are at a higher risk of infection than circumcised men.   This is due to the fact that underneath the foreskin of the penis is a mucus membrane that creates cells that HIV can infect; however, men who are circumcised do not create those cells since that mucus membrane basically turns into skin after circumcision.  This doesn’t mean run out and get circumcised though.  The only time that a circumcised man will not create those cells is if he was circumcised shortly after birth, not as an adult.

As far as sex with women goes, risk will be significantly increased if she is menstruating.  This is true for both partners.  For the person having sex with the woman, menstrual fluid has very high concentrations of the virus.  For the woman who is on her period, she is more susceptible at that time.

Having another STD will increase the risk of infection with HIV.  There are a variety of reasons for this.  Depending on the STD, the reason will be different.  For STDs which have sores associated with them (herpes, syphilis, etc.), it provides a pathway for HIV to enter.  For STDs that irritate mucus membranes (gonorrhea, chlamydia, etc.), this provides a more susceptible route for HIV infection.  Also, the immune response your body is having to the STD will increase likelihood of infection with HIV.  If the person who is HIV positive also has another STD, he or she will “shed” up to five times more viruses during sexual activity than he or she would without the STD.

Another factor that determines risk is the person’s viral load.  The viral load is the number of viruses per milliliter of blood.  Viral load is typically highest shortly after initial infection and at the end stages of the disease.  Current treatments for HIV often reduce viral load as well.  A person with a low viral load is less likely to pass the disease than someone with a high viral load.  This doesn’t mean because someone’s viral load is undetectable by current tests that they are not infectious, but it does decrease the risk.  Something to remember about viral load, though, is it’s frequently in flux.  A person’s viral load may be undetectable one day, and then detectable the next.  Also, the viral load in blood does not always correspond to the viral load in other fluids.



Transmission from mother to baby generally occurs during the birth, not while in the fetus, so a c-section and proper drug therapy often will mean the baby does not get infected.  Transmission may also occur during breast feeding.


Ways You Definitely Can’t Get It

The virus does not like the open air and dies pretty quickly (within a few minutes) and it is not transmitted by saliva, through skin pores or exhaled air, so casual contact (hugging, sharing glasses, etc.) with an infected person will not lead to transmission.  You can also not get it from insects (i.e. mosquitoes, lice, ticks, etc.) or any other animal.  Apparently, the virus doesn’t like non-human bodies very much either and dies very quickly (thus why the “H” is HIV stands for “Human”).  Most professional piercing places and tattoo places adhere to safety standards, including always using new or thoroughly cleaned needles, so those are typically safe.  Non-professionals may not adhere to those standards, so you need to be aware that possible transmission could occur.  Also, due to extensive testing and screening of the blood supply, you’re more likely to get hit by lightening than to get HIV from a blood transfusion.  Finally, you can only catch HIV from someone who already has the virus; it does not appear spontaneously.  Remember, the virus doesn’t care if you are male, female, gay, straight, white, black or purple; everyone is at risk.


What is Risk?

When we talk about risk associated with HIV infection, the term becomes rather confusing.  When one says “high risk” versus “low risk,” what does that exactly mean?  When we talk about risk with HIV, the risk is determined by a number of factors.  To make sense of it, let’s think about the risks associated with crossing the street and getting hit by a car.  Although the percentages of risk do not exactly line up, it makes a good reference for illustration.  Think of HIV as a car, and your risk of getting hit by a car under certain circumstances.  Under the right conditions, your chance of getting hit by a car are much greater than in other ways.  For example, crossing a busy highway at night is going to carry a much greater risk than crossing a country road during the day.  I created the following table as a way of getting an idea how risky each behavior is.


Equivalent “crossing the road and getting hit by a car” risk

Unprotected receptive anal or vaginal sex (the one getting fucked) when the guy ejaculates inside the person OR when sharing needles

A busy four-lane highway, at night.

Unprotected receptive anal or vaginal sex when the guy does not ejaculate inside the person

A busy four-lane highway, during the daytime.

Unprotected insertive anal or vaginal sex (the one doing the fucking), regardless of ejaculation

A busy two-lane highway, during the daytime.

Unprotected oral sex on a man with ejaculation with cuts/sores in the mouth

A downtown street in a small town, during a busy period of traffic, during the daytime.

Unprotected oral sex on a man with ejaculation, without cuts/sores in the mouth

A downtown street in a small town, during a slow period of traffic, during the daytime.

Unprotected oral sex on a man without ejaculation, with cuts/sores in the mouth OR unprotected oral sex on a woman with cuts/sores in the mouth

A side street in a small town, during a slow period of traffic, during the daytime.

Unprotected oral sex on a man without ejaculation, without cuts/sores in the mouth OR unprotected oral sex on a woman without cuts/sores in the mouth

A country road, during a slow period of traffic, during the daytime.

Receiving oral sex (whether male or female)

A blocked-off service road that has been closed for years, during the daytime.

Deep kissing, rimming or mutual masturbation

A forest path where no cars have ever been.

If another STD is present for any of the above activities

Add while wearing a blindfold.

If condoms/dental dams are properly used for the above activities

Add being assisted by a crossing guard carrying a big flashing “STOP” sign and a bullhorn.

Another important point to remember about the above table is it assumes you are doing these activities with someone who is HIV positive.  If the person is HIV negative, it would be equivalent to the risk of being hit by a car that doesn’t exist. 

As you may have guessed, with the above examples of being hit by a car, if you do that activity once, you most likely will not get hit, although it’s still possible.  However, if you frequently cross the street under those circumstances, the chances of getting hit by a car will become greater.  The same stands true of HIV, one exposure will possibly, but not usually, lead to infection; however, repeated exposures increase the risk. 

Also, the longer you stand in the middle of the road, the more likely you’ll be hit by a car.  Same with HIV, the longer you are exposed to the virus, the more likely you’ll get hit.  So, if you go down on a guy for a minute, your risk will be less than if you sucked him off for a half an hour. 

You can also think of someone who is positive’s viral load as the gas in the car.  If the car is running low on gas, the chance is greater that it’ll run out of gas and stop before it hits you.  If a person’s viral load is low, the chances are less that you will get infected, but still very much exist.