HIV and STIs: Why Other Infections Raise Risk

Other sexually transmitted infections raise your risk of getting and passing HIV, mainly because they cause inflammation and open sores that give the virus an easier entry point. An STI like syphilis, herpes, or gonorrhea draws immune cells to the genitals, the cells HIV targets, and any break in the skin or mucous lining lets HIV cross more easily. Treating STIs is part of HIV prevention.

How HIV is transmitted, and why STIs make it easier

HIV is a virus that attacks the immune system, and it only passes through certain body fluids: blood, semen, vaginal fluid, rectal fluid, and breast milk CDC. The main routes are anal or vaginal sex, sharing needles or injection equipment, and from a pregnant or breastfeeding parent to the infant. Saliva, sweat, tears, and urine don't carry enough virus to infect, so the fluid has to reach a mucous membrane (the rectum, vagina, penis, or mouth) or a break in the skin, or go directly into the bloodstream.

Other STIs change the math. Many cause inflammation, sores, or ulcers in the genital and rectal tissue, and that does two things at once. Sores from infections like syphilis or genital herpes break the protective barrier of the skin and lining, giving HIV a direct doorway. Inflammation from any STI, including gonorrhea and chlamydia, recruits white blood cells (especially CD4 T-cells) to the area, and those are the very cells HIV docks onto and infects. More target cells in one spot means a higher chance the virus takes hold.

The effect runs both ways. A person who already has HIV and picks up another STI often sheds more HIV in their genital fluids, because the inflammation pulls infected cells to the surface, so an untreated STI can raise how infectious someone is as well as how susceptible. Clinicians screen for and treat STIs aggressively as part of HIV care and prevention.

The risk is highest right after someone is infected

HIV moves through three stages: acute infection, chronic infection (clinical latency, which can last a decade or more untreated), and AIDS, the most severe stage, defined by a CD4 count under 200 cells/mm³ or an opportunistic infection CDC. The acute stage is dangerous and easy to miss. About 90% of people get flu-like symptoms 2 to 4 weeks after infection — fever, sore throat, swollen glands, rash — exactly when the viral load peaks above a million copies/mL and onward transmission is at its highest StatPearls. Someone in this window who also has an active STI is, biologically, at the peak of being able to transmit. Early symptoms after a risky exposure deserve an urgent test rather than a wait-and-see.

How HIV is NOT transmitted

HIV doesn't survive long outside the body, so the everyday contacts people worry about don't pass it. You cannot get HIV from:

• Toilet seats, doorknobs, gym equipment, or other surfaces.
• Sharing towels, sheets, clothing, dishes, or cups.
• Hugging, shaking hands, or other casual contact.
• Saliva, kissing, sneezing, or coughing — closed-mouth kissing carries no risk.
• Food or water, swimming pools, or hot tubs.
• Mosquitoes, ticks, or other insects.
• Donating blood (in the US, needles are sterile and single-use).

The same logic applies to STIs that scare people about HIV. Catching herpes or HPV from a surface or a toilet seat isn't how HIV spreads. HIV needs the specific fluids and a mucous or bloodstream route.

Who's at higher risk

About 38,800 people were newly diagnosed with HIV in the US in 2023, and an estimated 1.12 million are living with it CDC, 2023. The burden isn't spread evenly. Diagnosis rates cluster in the South and the capital — highest in Washington DC, then Georgia, Florida, and Louisiana. Higher-risk groups include men who have sex with men, people with a recent or current STI (because of the biological link above), people who inject drugs and share equipment, those with multiple partners or a partner of unknown HIV status, and people who exchange sex for money or drugs. Having any STI is itself a flag to test for HIV, since co-infection is common when the two share routes and one amplifies the other.

Mother-to-baby transmission can be nearly eliminated

HIV can pass to an infant during pregnancy, childbirth, or breastfeeding, but this route is highly preventable. With antiretroviral therapy (ART) during pregnancy and labor, plus preventive medicine for the newborn, the risk of mother-to-child transmission can be reduced to less than 1%. Untreated STIs during pregnancy can complicate this, one more reason prenatal STI screening matters. If you want the detail on infant treatment and outcomes, see is early hiv treatment in babies safe and effective.

Reducing the risk

Because STIs raise HIV susceptibility, the most protective thing you can do is reduce both at once. The CDC's core prevention tools are condoms, PrEP, PEP, treatment-as-prevention (U=U), and regular testing. Condoms, used consistently, block the fluid exchange that both HIV and most STIs need.

PrEP (pre-exposure prophylaxis) is daily or long-acting medicine for people without HIV who are exposed through sex or injection drug use. Taken as prescribed, it reduces HIV risk from sex by about 99% and from injection drug use by at least 74% CDC. Daily oral options are Truvada and Descovy, and there's a long-acting injectable, cabotegravir (Apretude). Descovy isn't approved for people at risk through receptive vaginal sex, while Truvada covers all exposure routes. PrEP requires a confirmed HIV-negative test before starting and ongoing follow-up, because starting it with undiagnosed HIV risks drug resistance. Newer long-acting options change the picture: twice-yearly injectable lenacapavir produced zero infections among women in a major trial WHO.

For people already living with HIV, treatment is prevention. Someone who takes ART and stays virally suppressed (undetectable) does not transmit HIV to sex partners. This is U=U, backed by data. Across the PARTNER studies, mixed-status couples logged more than 125,000 condomless sex acts with zero linked transmissions while the HIV-positive partner was undetectable Lancet. Most people reach undetectable within about six months of starting ART CDC. U=U covers HIV only and doesn't protect against other STIs, so condoms still matter. To understand how starting treatment early helps the whole community, read earlier hiv treatment can help prevention.

How the prevention tools compare

If you may have been exposed

PEP (post-exposure prophylaxis) can prevent HIV from taking hold, but it must start within 72 hours of the exposure and is taken daily for 28 days CDC. Treat it like an emergency — an urgent-care or ER conversation tonight, not a wait-and-test one. After the PEP window, or if you simply want to know your status, check the timing in when to test after exposure.

When to see a clinician

Get HIV and STI testing if you've had a possible exposure, have symptoms of a new STI (sores, discharge, burning, unusual rash), are starting a new relationship, or simply haven't been screened. The USPSTF gives HIV screening its strongest recommendation: test all adolescents and adults ages 15 to 65 at least once, and repeat for those at increased risk — at least annually per CDC USPSTF. Early symptoms can look exactly like the flu, and many people have none at all, so symptoms can neither confirm nor rule out HIV. Only a test can. You can get tested confidentially, and modern HIV is a manageable, long-term condition: a 20-year-old who starts treatment before their CD4 falls below 200 has a life expectancy approaching the general population's Lancet HIV.