HIV Transmission

Understanding HIV Transmission - How HIV is Passed from Person to Person

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Table of Contents

The Human Immunodeficiency Virus (HIV) is the trigger of the immunodeficiency disease AIDS. Although HIV / AIDS can be treated well nowadays, it is still incurable. This makes it all the more important to know the transmission pathways of the virus and how to protect oneself against infection.

How is HIV transmitted?

HIV is transmitted exclusively through body fluids: the concentration of HI viruses is highest in blood, sperm and the secretions of the anal mucosa, and these body fluids pose the greatest risk of infection. A lower probability of infection is given by contact with vaginal secretion and breast milk. Saliva, sweat, tear fluid, urine and stool are not infectious. Although these body secretions contain viruses, they are too small to lead to infection.

Potential entry points for HIV are fresh wounds, mucous membranes (especially the vaginal and anal mucous membranes) and vulnerable areas of the outer skin, such as the glans and the inside of the foreskin. In addition to the common use of needles for intravenous drug use ("needle sharing"), unprotected sexual intercourse is the main route of HIV transmission. The condom therefore remains the safest way for sexually active persons to protect themselves from HIV and other sexually transmitted diseases.

HIV Transmission

When is unprotected sex particularly risky?

Different sexual practices have different risks of infection. In the majority of cases, receptive (receiving) sex represents a greater risk than insertive (penetrating) sex. In vaginal intercourse, for example, the receiving woman has a greater risk than the insertive partner. In principle, the risk of HIV infection during sexual intercourse is greatest when small, often invisible injuries occur. Infectious semen or vaginal fluid can then enter the bloodstream directly.

In general, a fresh or untreated HIV infection or the presence of additional sexually transmitted infections (e.g. genital herpes or syphilis) poses a higher risk. A lower risk exists, for example, if the HIV virus has fallen below the detection limit as a result of appropriate therapeutic measures. However, there is no risk of transmission when kissing or sharing sanitary facilities.

Risk during vaginal intercourse

Contrary to widespread assumptions, unprotected vaginal intercourse is the most common means of HIV transmission. The risk is greater for women than for men, because on the one hand sperm contains a much higher HIV concentration than vaginal secretion, and on the other hand the woman comes into contact with more body fluid (sperm). The surface of the mucous membrane in the vagina, which in this case is the entry port for the virus, is also much larger than the surface of the skin at the tip of the glans. During menstruation, the risk of contracting HIV during unprotected vaginal intercourse increases many times over for both partners.

Oral intercourse

Oral intercourse means caressing and stimulating the genital area of one's partner with the mouth. The following love plays are distinguished:


In cunnilingus, the outer genital area of the woman (labia, clitoris and vaginal entrance) is stimulated with the mouth. Usually the virus concentration absorbed in this way with the vaginal fluid is not sufficient for infection. Apart from this, the oral mucosa is not very sensitive. In the case of small injuries in the pubic area or in the mouth or during menstruation, however, contact with blood can lead to HIV infection. So-called dental dams can be used to protect against infection. These wafer-thin cloths made of latex or polyurethane are placed over the outer genital area and, like condoms, are available in various variations.


A slightly higher risk of infection exists with fellatio, the oral stimulation of the penis. If ejaculation occurs in the oral cavity, the HI virus can be absorbed through the oral mucosa or through small injuries in the oral cavity. However, HIV transmission via fellatio has so far only been documented in isolated cases.

Oral anal intercourse

An infection via oral-anal intercourse, the stimulation of the anus with the tongue, should not be possible with intact skin at the anus. Care should be taken with haemorrhoids and possible ulcers in the gastrointestinal tract, as blood can get into the stool.

Anal intercourse

The intestinal mucosa is very sensitive and can easily be injured during anal intercourse. During anal intercourse with an HIV-positive partner, the virus penetrates through tiny cracks in the intestinal mucosa or anus. Since the HIV concentration in the secretions of the intestinal mucosa is usually even higher than in blood and sperm, there is also a relevant risk of transmission during insertive anal intercourse, i.e. for the invading partner. Tiny, invisible injuries to the penis or glans increase this risk.

Sadomasochistic sexual practices

Since the intact skin offers sufficient protection against HIV, no transmission can occur when stimulating the vagina, penis and anus with the hand. Ejaculation or urinating on the skin is also harmless. Caution is required, however, as soon as blood is involved or as soon as sexual practices can lead to small injuries that are not visible - for example in the vagina.

Sex toys

Dildos, vibrators and other sex toys should always only be used by one person or when used by several people with a condom. It is best to clean them thoroughly with a disinfectant solution before passing them on.

What can be done in case of sex accidents?

  1. If an unwanted ejaculation occurs in the mouth, spit out the sperm as quickly as possible and rinse the mouth with a disinfectant solution or alcohol.
  2. However, you should refrain from rinsing if a condom bursts in the vagina or an unwanted ejaculation occurs in the vagina. Flushing only transports the viruses further into the vagina. By the way, there are also HI viruses in the lust droplet - albeit in lower concentrations. The lust droplet is a clear liquid that enters the urethra before ejaculation and is secreted shortly before ejaculation.
  3. If blood, semen or vaginal fluid has reached a wound, the wound should be rinsed well with water and disinfected for several minutes.
  4. If a risk contact has occurred, post-exposure prophylaxis (PEP) is a medicinal measure that can often be used to avert an HIV infection. It is important that PEP is administered as quickly as possible.

Other ways of HIV transmission

Infected Blood Transfusions

The HIV can be transmitted through infected blood transfusions or infected organ transplants, although this type of transmission has become very rare because of advanced screening tests.

Dirty/ Non-Sterile Needles

Since HIV is transmitted via blood, sharing needles/syringes with an infected person can easily cause infection. Believe it or not, HIV can live in a used needle for up to 42 days! 100% sterile needles are only found in a sterile medical environment and are only used once before being disposed of.

Pre-Chewed Food

This circumstance has only ever been known among mother/infants and is obviously a very rare circumstance. When infected blood from a caregiver’s/mother’s mouth mixes with food while chewing, the chances of spreading HIV rise.

Bite Wounds

HIV can be spread if bitten by a person positive for the disease. There were only a limited number of cases, and each involved severe tissue damage leading to open wounds. There haven’t been any cases of transmission when the skin hasn’t been broken.


HIV can also be spread from mother to child during pregnancy, childbirth, or be transmitted from the mother to the child when breastfeeding, though this is a less common method of transmission compared to those above.

Today, any physician will recommend simple testing to ensure the mother does not have an infection and be able to properly prepare if she does. Quick treatment and early detection has drastically lowered the amount of babies born in the US with the virus.

Contaminated Objects

It’s possible to contract the virus from an accidental (contaminated) needle stick, or a scrape from a sharp object with contaminated blood on it. This risk lies mainly with health care workers.

HIV Can’t Be Transmitted By or Contracted From:

  • Saliva, sweat or tears
  • Water or air
  • Insects or pets
  • Toilet surfaces, food & drinks
  • Closed mouth kissing
    • It is extremely rare for HIV to be transmitted by open mouth kissing, and only if the HIV positive party has open, bleeding sores in their mouth. The virus can’t be transmitted via saliva.

HIV Outside of the Body

Though HIV can live within a dirty/used needle for up to 40+ days in certain conditions, it doesn’t survive well outside the body, and can’t reproduce without a human host. The virus can’t be transmitted, transferred or spread by:

  • Insects, such as mosquitos, lice or ticks
  • Saliva, sweat or tears
  • Unbroken skin to skin contact, such as hugging or shaking hands
  • On the surface of clothing, without the presence of blood
    • HIV can’t be spread either to or contracted from any animals (outside of humans) or pets.

Additional Resources

HIV InSitehivinsite.ucsf.eduHIV InSite has comprehensive, up-to-date information on HIV/AIDS treatment and prevention.
NHSwww.nhs.ukNHS is the UK's biggest health website with topics related to HIV/AIDS.
Stanford Health Carestanfordhealthcare.orgStanford Health Care provides HIV patients with the very best in diagnosis and treatment.
Lab Tests Onlinelabtestsonline.orgLab Tests Online provides information on HIV testing as well as FAQs on what to expect when getting tested. provides vital HIV services where they are most needed.


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