Condoms and dental dams help prevent sexually transmitted infections (STIs), including HIV, from being transmitted between sexual partners. STIs can be transmitted between partners during different types of sex without a condom, including anal sex, vaginal sex, and oral sex.

Having sex without condoms can carry certain risks depending on how many partners you have and the type of sex you’re engaging in.

Read on for key information that everyone who has sex without condoms should know.

The Food and Drug Administration (FDA) reports that millions of people in the United States contract an STI each year. Using condoms during sex reduces the risk of transmission of most STIs, including HIV, gonorrhea, chlamydia, syphilis, and certain types of hepatitis.

It’s possible to contract an STI and not see symptoms for days, months, or even years. If left untreated, some STIs can cause significant health issues. This can include damage to major organs, infertility issues, complications during pregnancy, and even death.

The risk of contracting an STI is higher for people who have multiple sexual partners. Individuals can reduce the risk by using condoms consistently and by getting tested for STIs before each new partner.

When sexual partners decide to have condomless sex — or “barrier-free” sex — exclusively with each other, they are sometimes referred to as “fluid-bonded.”

If fluid-bonded sexual partners have been tested, and the test results show no STIs, then engaging in sex without barriers is considered to carry little to no risk of STIs. This depends on the accuracy of STI test results and all fluid-bonded partners only having sex with each other.

Keep in mind, certain STIs, such as human papilloma virus (HPV), aren’t always included in a standard STI test. Planned Parenthood suggests that people who are fluid-bonded still get tested regularly for STIs.

Your doctor can tell you more about how often it makes sense for you to get tested for STIs.

The risk of contracting HIV is higher for people living with an STI, particularly syphilis, herpes, or gonorrhea.

STIs cause inflammation that can activate the same immune cells HIV likes to attack, and allow the virus to replicate more quickly. STIs can also cause sores that make it easier for HIV to enter the bloodstream.

HIV can be transmitted via the mucous membranes of the penis, vagina, and anus. It can also potentially be transmitted through cuts or sores on the mouth or other areas of the body.

Condoms and dental dams provide a physical barrier that can help prevent HIV transmission. When people engage in sex without condoms, they don’t have that layer of protection.

The Centers for Disease Control and Prevention (CDC) reports that condoms are highly effective at preventing HIV transmission as long as you use them every time you have sex. Latex condoms offer the most protection against transmission of HIV. If you’re allergic to latex, the CDC says that polyurethane or polyisoprene condoms also reduce the risk of HIV transmission, but they break more easily than latex.

When a person contracts HIV, there’s a window period from the time of exposure to the virus until the time it will show up on an HIV test. Someone who has an HIV test during this window may receive results that say they are HIV-negative, even though they have contracted the virus.

The length of the window period varies depending on biological factors and the type of test being used. It generally ranges from one to three months.

During the window period, a person who has contracted HIV can still transmit it to other people. That’s because levels of the virus are actually higher at this point, even though HIV tests may not be able to detect it yet.

The likelihood of HIV being transmitted during sex varies depending on the type of sex involved. For example, the level of risk is different for anal sex compared to oral sex.

HIV is most likely to be transmitted during anal sex without a condom. That’s because the lining of the anus is more prone to rips and tears. This can allow HIV to enter the bloodstream. The risk is higher for the person receiving anal sex, sometimes called “bottoming.”

HIV can also be transmitted during vaginal sex. The lining of the vaginal wall is stronger than the lining of the anus, but vaginal sex can still provide a pathway for HIV transmission.

Oral sex without a condom or dental dam carries a relatively low risk of HIV transmission. If the person giving oral sex has mouth sores or bleeding gums, it is possible to contract or transmit HIV.

For couples who are fertile and engaging in “penis-in-vagina” sex, having sex without a condom increases the risk of an unplanned pregnancy.

According to Planned Parenthood, condoms are 98 percent effective at preventing pregnancy when used perfectly every time, and around 85 percent effective when used normally.

Couples who have sex without condoms and wish to avoid pregnancy can consider an alternate form of contraception, such as an IUD or the pill.

The only forms of birth control that prevent against STIs are abstinence and condoms. Birth control methods like the pill, the morning-after pill, IUDs, and spermicide don’t prevent the transmission of viruses or bacteria.

Condoms are highly effective at preventing the transmission of HIV and other STIs — but they only work if they’re used correctly.

To use a condom effectively, always start to use it prior to sexual contact because bacteria and viruses can be transmitted through pre-ejaculate and vaginal fluid. Make sure only to use water-based lubricants with a condom. Oil-based lubricants can weaken latex and cause the condom to break.

If you and your partner are having sex in multiple ways — such as anal, vaginal, and oral sex — it’s important to use a new condom each time.

Sex without condoms increases the risk of STI transmission between partners. For some couples, pregnancy is also a risk of condomless sex.

You can reduce the risk of exposure to an STI by using condoms consistently every time you have sex. It also helps to get tested for STIs before sex with each new partner. Your doctor can provide guidance about how often to get tested for STIs.