HIV is a virus that attacks the body’s immune system. Acquired Immunodeficiency Syndrome (AIDS) is the most advanced stage of HIV infection. Transmission of HIV is possible during sexual activity, and the presence of blood, including menstrual blood, can influence the level of risk involved.
How HIV Transmission Occurs
HIV transmission depends on the exchange of specific bodily fluids from a person with a detectable viral load to another. These fluids include blood, semen, pre-seminal fluid, vaginal fluids, rectal fluids, and breast milk. The virus must enter the bloodstream of the uninfected partner to cause infection.
Entry usually occurs through mucous membranes, the delicate linings found in the vagina, rectum, and the opening of the penis. While intact skin is an effective barrier, these membranes are thinner and susceptible to microscopic tears. Any open cuts, sores, or inflammation in the genital or rectal area can also provide a direct pathway for the virus to enter the body.
The concentration of the virus, known as the viral load, in the transmitting partner’s body fluids determines the likelihood of transmission. A higher viral load means a greater amount of the virus is present in the fluids exchanged, increasing the risk of transmission through sexual contact.
Understanding the Risk Associated with Menstrual Blood
Menstrual blood is composed of shed uterine lining and blood, and thus can contain HIV if the person is living with the virus and has a detectable viral load. Studies suggest that the viral concentration of HIV in cervico-vaginal fluid may fluctuate throughout the menstrual cycle. The level of the virus may be highest around the time of menstruation, increasing the risk of transmission to a sexual partner during this period.
The presence of blood introduces a greater volume of fluid containing the virus into the sexual encounter. This is relevant during penetrative sex, where the blood contacts the partner’s mucous membranes. Additionally, the tissues lining the vagina and cervix undergo changes during the menstrual cycle.
Some research indicates that hormonal shifts during the menstrual cycle may temporarily reduce the local immune defenses in the female reproductive tract. This temporary suppression could create a brief “window of vulnerability” where the likelihood of acquiring the virus is potentially enhanced. Furthermore, friction from sexual intercourse, especially compounded by blood, can lead to small, unseen micro-abrasions in the delicate tissues of the vagina or rectum.
These tiny tears act as easier entry points for the virus to access the bloodstream. Therefore, the specific biological and physical factors present during menstruation can elevate the baseline risk of transmission when one partner has a detectable HIV viral load.
Essential Strategies for Risk Reduction
The most effective way to prevent the sexual transmission of HIV is through consistent prevention strategies. Barrier methods, such as external or internal condoms, provide a physical shield that prevents the exchange of bodily fluids. Using condoms correctly and every time sexual activity occurs significantly reduces the risk of transmission.
Knowing the HIV status of both yourself and your partner is important for managing risk. Regular testing allows individuals to start treatment immediately if they are diagnosed with HIV. For HIV-negative people at high risk of exposure, Pre-Exposure Prophylaxis (PrEP) is a medication that can be taken daily or on demand.
PrEP is highly effective, reducing the risk of acquiring HIV from sexual activity by about 99% when taken as prescribed. For someone who has been recently exposed to HIV, Post-Exposure Prophylaxis (PEP) is a course of antiretroviral drugs that must be started within 72 hours of the exposure to prevent infection.
For people living with HIV, the most powerful prevention tool is adhering to antiretroviral therapy (ART). Taking ART as prescribed reduces the amount of virus in the blood to an undetectable level. A person who maintains an undetectable viral load cannot transmit HIV through sex, a concept summarized by the public health message Undetectable = Untransmittable, or U=U.