2025 World AIDS Day Special: The Science Behind HIV Transmission Through Bodily Fluids And How That Influences Risk

Even decades into awareness, HIV remains one of the most misunderstood infections, not because of the virus per se, but because of persistent myths about how it is spread. Many people continue to overestimate casual transmission risks or underestimate real ones. The theme for 2025 World AIDS Day is "Overcoming disruption, transforming the AIDS response".

Ahead of the day, let's take a look at the science behind HIV transmission via bodily fluids, so you can separate fact from fear and make informed, safe choices.

What Makes HIV Infectious?

The human immunodeficiency virus or HIV attacks the body's immune system. More specifically, it attacks a subgroup of lymphocytes called CD4 cells.

“HIV does not live for a long time outside the body and requires a direct entrance into the bloodstream. That is why the virus is only transmitted through certain bodily fluids; those that contain enough of the virus to infect another person,” says Dr. Maheshkumar M. Lakhe, Infectious Diseases Physician, Dr Lakhe's Healthcare and Research Centre.

• Major fluids proven to transmit HIV include:
• Blood
• Semen and pre-seminal fluid
• Vaginal and rectal fluids
• Breast milk

Infection with any of these fluids can contain high viral loads; they are infectious only when directly coming into contact with mucous membranes (which are present in the rectum, vagina, penis, and mouth), with damaged tissue, or injected directly into the blood (as via a needle).

However, there are certain fluids that do not transmit the virus. HIV cannot be passed on through saliva, sweat, tears, or urine. These fluids carry too little virus to pose any risk. He clarifies, “Casual contact, sharing meals, or even touching people with HIV are totally safe.”

How Transmission Occurs

1. Unprotected sexual contact: Infectious Diseases Physician Dr. M. Lakhe says this is the most common route of HIV transmission. During vaginal or anal intercourse, HIV can enter through the mucous membranes if one of the partners is infected and not treated. The risk increases when there are other STIs that cause inflammation or sores to facilitate entry.
2. Sharing needles or syringes: The use of drugs by injection is another highly dangerous route. “Needles contaminated with even the tiniest amount of infected blood can directly introduce the virus into another person's bloodstream,” says the expert.
3. Mother-to-child transmission: HIV can be transmitted from an infected mother to her baby during pregnancy, childbirth, or breastfeeding. Early diagnosis and ART can reduce this risk to less than 1%.
4. Blood transfusions or organ transplants: All donated blood and organs are checked for HIV in India and most countries today, so this route is extremely rare.

“The risk of transmission is highly dependent on the level of virus in the body of the infected individual, referred to as the viral load. Those on effective ART are able to reduce their viral load to undetectable levels, and effectively become unable to transmit HIV sexually,” says Dr. M Lakhe. This concept (known as U=U, or Undetectable = Untransmittable) makes up one of the most significant messaging breakthroughs in public health.

The most effective weapons against HIV are knowledge and preventive care. Safe sexual practices, including condoms, reduce risk. For people at higher risk, a medication called preexposure prophylaxis, or PrEP, can prevent infection if taken regularly. Regular testing is very important, since early diagnosis and treatment not only protect health but also stop further spread of the virus.

Read more:

1. Assam’s HIV Positive Woman Turns Personal Tragedy Into Collective Empowerment
2. Maldives Becomes World's First Country To Achieve ‘Triple Elimination’ Of Mother-To-Child Transmission Of HIV, Syphilis And Hepatitis B
3. 'Test Before You Wed': Doctor Yalgi Revives HIV Awareness Campaign In Karnataka