Pre-exposure prophylaxis (or PrEP) is a way for people who do not have HIV but who are at very high risk of getting HIV to prevent HIV infection by taking a pill every day. The pill (brand name Truvada) contains two medicines (tenofovir and emtricitabine) that are used in combination with other medicines to treat HIV. When someone is exposed to HIV through sex or injection drug use, these medicines can work to keep the virus from establishing a permanent infection.

When taken daily, PrEP is highly effective for preventing HIV. Studies have shown that PrEP reduces the risk of getting HIV from sex by about 99% when taken daily. Among people who inject drugs, PrEP reduces the risk of getting HIV by at least 74% when taken daily. PrEP is much less effective if it is not taken consistently.

As PrEP only protects against HIV, condoms are important for the protection against other STDs.

Condoms are also an important prevention strategy if PrEP is not taken consistently.

It is generally accepted that having a sexually transmitted disease (STD) increases in a person’s risk of getting HIV, both for biological and behavioral reasons.

According to research, STDs like syphilis and gonorrhea not only provide HIV easier access to vulnerable cells and tissues of the body, STD co-infection actually increases the infectivity of the person with HIV—making them more likely to transmit the virus to others.1

STDs can increase HIV susceptibility in a number of ways:2

Some STDs cause open wounds or ulcers to form in the genital area (such as syphilis, which frequently presents with ulcerative chancres). These wounds, sometimes seen and sometimes not, provide HIV a direct route into the bloodstream.
While some STDs don’t cause open wounds, the presence of the infection can cause the body to increase the concentration of CD4 T-cells in the genital area. It has been well established that increased concentrations these cells can provide HIV with a favorable target for infection.
People infected with an STD also have increased concentrations of HIV in their seminal and vaginal fluids, increasing the possibility of HIV transmission.
Prime among the concerns are STDs like infective syphilis, gonorrhea, and herpes (HSV), with evidence that chlamydia can also increase HIV risk in women.1

STD Statistics in the U.S.
According to the Centers for Disease Control and Prevention (CDC), nearly 20 million new STD infections occur every year, accounting for almost $16 billion in health care costs.3 In 2017, the bulk of infections were primarily constrained to three diseases:

Chlamydia: 1,708,569 infections at a rate of 529 per 100,0004
Gonorrhea: 555,608 infections at a rate of 172 per 100,0005
Syphilis (primary and secondary): 30,644 infections at a rate of 9 per 100,0006
The rate of STD infections is particularly high among gay and bisexual men who, not surprisingly, account for the highest rate of HIV infections in the U.S.

Gay and bisexual men account for almost all primary and secondary syphilis cases.

To this end, If you are a sexually active gay or bisexual man, you should be tested for syphilis, chlamydia, gonorrhea, and HIV at least once a year. More frequent STD testing, between every three to six months, is recommended for gay or bisexual men at high risk, especially those who have multiple sex partners, use recreational drugs, or practice condomless sex.

Benefits of STD Screening and Treatment
In the presence of an STD diagnosis, people should receive treatment as soon as possible—not only to treat the infection but to potentially decrease the risk of onward transmission should you have HIV.

According to the latest research, HIV-positive people on STD therapy tend to shed far less HIV and to shed the virus less frequently than those not on treatment. 3(Shedding is the state where the HIV is present in semen, vaginal secretions, blood, or breast milk even when a person has an undetectable HIV viral load).

Additionally, safer sex counseling hand-in-hand with STD therapy can help a person uninfected with HIV to identify their personal risk factors and find ways to better reduce their risk of HIV.

A Word From Verywell
Oftentimes, we tend to focus on HIV in isolation, particularly when it comes to issues of prevention and treatment. But the fact is this: even if a person is on the HIV prevention pill (PrEP) or is taking full-time antiretroviral therapy, STDs can increase the risk of HIV transmission, putting yourself or others at risk.

It is, therefore, important to remember the following take-home points:

You have a greater chance of HIV if you have an STD.
Having an STD and HIV can increase your risk of spreading HIV.
STD treatment may help slow the spread of HIV.
HIV therapy does not prevent you from getting another type of STD.
Condoms are still the single best way to reduce your risk of getting an STD, including HIV.

Undetectable = untransmittable is the message of a new UNAIDS Explainer. With 20 years of evidence demonstrating that HIV treatment is highly effective in reducing the transmission of HIV, the evidence is now clear that people living with HIV with an undetectable viral load cannot transmit HIV sexually.

Three large studies of sexual HIV transmission among thousands of couples, one partner of which was living with HIV and the other was not, were undertaken between 2007 and 2016. In those studies, there was not a single case of sexual transmission of HIV from a virally suppressed person living with HIV to their HIV-negative partner. The Explainer cautions, however, that a person can only know whether he or she is virally suppressed by taking a viral load test.

For many people living with HIV, the news that they can no longer transmit HIV sexually is life-changing. In addition to being able to choose to have sex without a condom, many people living with HIV who are virally suppressed feel liberated from the stigma associated with living with the virus. The awareness that they can no longer transmit HIV sexually can provide people living with HIV with a strong sense of being agents of prevention in their approach to new or existing relationships.

The new UNAIDS Explainer series aims to inform readers about key or emerging issues in the AIDS response. With recommendations for programme managers and advice for national responses, they are short but informative snapshots of the current knowledge about an area of the AIDS response.