All the Facts on the Most Common STIs

You probably already know sexually transmitted infections are extremely common. The CDC estimates there are 19.7 new STI diagnoses in the U.S. every year, and more than half of all sexually active people will have an STI at some point in their life. Considering this, and the fact that most people probably don’t get the best education on STIs in school, it’s probably in your best interest to at least have the basic info down. Here’s a thorough breakdown on how to detect, get tested, and get treated for nine of the most common STIs.


Chlamydia is a bacterial infection that can occur in the vagina, cervix, penis, anus, urethra, eyes, or throat. It’s one of the most common STIs and often doesn’t show any visible symptoms — which is why it’s recommended that women under age 25 be routinely tested for it once a year. It’s spread via skin-to-skin contact, and through having vaginal, anal, or oral sex with someone who has it. It’s also possible for pregnant women who have an infection to pass it to a baby during delivery.

What the symptoms are: Chlamydia is tricky because most people who have it don’t have any symptoms. But for those who do, there may be abnormal vaginal or penile discharge, swelling and pain in the testicles, and burning with urination. Anal infections can cause rectal pain, anal discharge, or bleeding near the rectum.

When you should be tested: Because it so rarely shows symptoms, you should be tested after having unprotected sex with a new partner, after having sex with someone who has chlamydia, or about once a year if you’e sexually active. Sexually active women under age 25 should be tested routinely. Leah Millheiser, an ob-gyn and director of the Female Sexual Medicine Program at Stanford University, said women in that age group are considered higher risk because of the type of cells that are exposed on the cervix at that time. Chlamydia can be tested with a urine or swab test that checks for chlamydia bacteria. Your doctor also might look at your cervix to see if there’s any chlamydia-related discharge present.

How it’s treated: Fortunately, chlamydia is easily treated with a round of antibiotics prescribed by your doctor. It’s important that any sexual partners you have also be treated for chlamydia when you are, or you’ll just keep passing the infection back and forth to each other. Millheiser said there’s something called “expedited partner therapy” that makes it easier for partners of people who are diagnosed with chlamydia to be treated. The legal nuances of EPT vary from state to state, but basically it allows your partner to get medication to treat chlamydia from your physician without having to be seen themselves. “In California, for example, if I have a female patient tell me her boyfriend doesn’t have a doctor I can give her an extra prescription,” Millheiser said.

If left untreated, chlamydia can cause serious health problems, especially in women. It can spread to the uterus and fallopian tubes can cause pelvic inflammatory disease, which can lead to pain, infertility, or ectopic pregnancy. That’s why it’s important to get tested if you have any reasons to suspect you’ve been exposed — it’s easily curable, and saves you from a lot of serious issues that may occur if left untreated.


Pubic lice are little parasites that attach to the coarse hair near your genitals. They’re usually called crabs because they look like tiny versions of… crabs. They’re super common and not dangerous, but they can be extremely itchy (and annoying). Crabs are spread through sexual contact with someone who already has them, and they’re not a sign of a lack of hygiene or dirtiness.

What the symptoms are: Crabs typically start showing symptoms about five days after you get them, and the first sign is usually irritation and intense itching around your pubic hair in reaction to the crab bites. You might also see little blue dots (those are the bites) or spot the little grayish-white bugs in your hair.

When you should be tested: Because they’re visible and have pretty distinct symptoms, you’ll probably be able to tell on your own if you have crabs. Even if you don’t have any symptoms and think you may have had sex with someone who has crabs in the past month, a doctor’s visit to check for crabs is a good idea. You can go anywhere from your general practitioner’s office to a Planned Parenthood clinic to be screened.

How it’s treated: There are several over-the-counter gels, shampoos, liquids, and even foams that treat crabs. Some common brands, according to Planned Parenthood, are A-200, Rid, and Nix. Any sex partners you’ve had in the past month should also treat themselves — even if they don’t have any symptoms — to avoid passing crabs back and forth. Just like you do with head lice, you’ll need to pick the eggs out of your pubic hair after completing whichever OTC treatment you choose. You can do that with your fingernails or a fine-tooth comb. You’ll also want to make sure any bedding, towels, and clothing you have are thoroughly cleaned by washing and drying a few times. If the crabs reappear 9-10 days after treatment, repeat the whole thing again. If they still won’t go away, talk to your doctor.


One of the most common STIs, Gonorrhea is a bacterial infection that doesn’t usually cause symptoms. Like chlamydia, it’s carried in semen, pre-ejaculate, and vaginal fluids, and can infect the vagina, cervix, penis, anus, urethra, throat, and — rarely — the eyes. Also like chlamydia, it’s recommended that women under 25 be screened for gonorrhea once a year because it’s so common. It’s spread mainly through vaginal, anal, and oral sex, or from mother to baby during delivery if a woman is infected at the time of birth. Even if you aren’t presenting symptoms, you can still spread the infection, which is why it’s so important to wear condoms and be tested regularly.

What the symptoms are: Most people don’t get symptoms with gonorrhea, or the symptoms are sometimes so mild they’re not noticeable. If you do get symptoms, they’ll probably show up within a week. People with vaginas might notice pain or burning with urination, abnormal discharge that’s yellowish or bloody, or spotting between periods. People with penises are more likely to have symptoms, which include yellow, white or green discharge from the penis, pain or burning with urination, or pain and swelling in the testicles. An anal infection usually doesn’t have symptoms, but when present they include itching in or around the anus, anal discharge, or pain with pooping. Again, symptoms are rare, but a throat infection usually just feels like a sore throat.

When you should be tested: Because there aren’t usually any symptoms, you should be tested annually for gonorrhea if you’re sexually active, or within two weeks if you think you’ve had sex with someone who has it. Gonorrhea can be tested with a urine sample, a sample of any discharge you may have, or sometimes with a swab of your urethra, vagina, or anus.

How it’s treated: Some strains of gonorrhea resist antibiotics and are hard to treat, but most infections are very treatable and go away easily with antibiotics. It’s incredibly important that any sex partners you have also get treatment when you do, so you don’t pass the infection back and forth or share it with other people. Expedited partner therapy is also available for gonorrhea treatment in most states. Your doctor will likely ask you to be tested again in three months to make sure the infection is gone. Getting tested and treated is important because gonorrhea can have serious health outcomes if it’s left untreated — it can spread to the uterus or fallopian tubes and cause pelvic inflammatory disease, which can lead to pain, infertility, and ectopic pregnancy. An untreated infection in a penis can spread to the epididymis and cause testicular pain.


There are five types of hepatitis — A through E — all of which are viral infections that cause inflammation of the liver. The most common types are hepatitis A, B, and C — hepatitis D only affects people who have hepatitis B. Hepatitis E is extremely rare in the United States. Each type can be contracted in a different way, including ways that don’t involve sex, but let’s just focus on the sexually transmitted possibilities for now.

Type B is the kind of that’s most likely to be spread through sex, according to Planned Parenthood. It’s very contagious, and is spread through infected blood, semen, and vaginal fluid. Type A is spread through anal-oral contact, Type C isn’t often spread through sex, and type D is passed through contact with infected blood or through sex with someone who has HIV. For more information on the other ways hepatitis can be spread, the CDC has a lot of information available that’s very easy to navigate even if you aren’t a doctor.

What the symptoms are: Though each type of hepatitis is caused by a different viral infection, they all share common symptoms. They usually show up within two to five weeks. These include mild flu-like symptoms, dark urine, jaundice (yellowing of the skin and whites of the eyes), and fever. Hepatitis A can also cause nausea, vomiting, and stomach pain.

When you should be tested: All types of hepatitis are diagnosed with a blood test. There are also preventative vaccines for hepatitis A and B. You should be tested if you’re having symptoms, or think you’ve come into contact with hepatitis either from having sex with someone who has it, having unprotected sex, or coming into contact with blood from someone who has it (by sharing a needle, a razor, or even a toothbrush). It might take up to two months for an infection test to be accurate, but Planned Parenthood says not to wait on seeing a physician if you’re not feeling well. Your doctor will help determine when you should be tested again if repeat tests are necessary.

How it’s treated: Hepatitis B can’t be cured but almost always goes away on its own within four to eight weeks, according to Planned Parenthood. Even after it goes away, about 1 in 20 people who have hepatitis B infections become carriers, meaning they have a chronic infection and are contagious for the rest of their lives. These chronic infections can lead to serious liver disease like cirrhosis and liver cancer.


There are two types of herpes — simplex virus-1 and simplex virus-2. Both are extremely common, and both can be spread via sex with someone who has it, or by skin-to-skin contact with an area that has active sores or lesions. According to Planned Parenthood, most people get it from someone who doesn’t have any active sores, but it’s most contagious when sores are present because fluid from the sores easily spreads the herpes virus.

What the symptoms are: Symptoms are important when it comes to herpes because a test is only truly accurate when someone has visible lesions that can be tested, or in other words, is experiencing an outbreak. The most common symptom you’ll see is sores on your genitals or mouth (like a cold sore). These sores usually show up within 2-20 days after getting infected and look like a group of blister-like bumps that are itchy and painful. They can show up on your vagina, vulva, penis, anus, and inside of your thighs. Infections caused by herpes simplex virus-2 can also have flu-like symptoms, like swollen glands, fever, chills, headache, or fatigue. But people with herpes also don’t have any symptoms most of the time, so it can be hard to figure out that’s what’s going on until you’re tested.

When you should be tested: Herpes tests are tricky. A lot of people who’ve never had an outbreak can test positive for low levels of the antibodies, which is why doctors prefer to test by swabbing a sore for an accurate test. You should be tested soon after you think you may have come into contact with herpes — a doctor can decide about re-testing or blood testing if you don’t have any sores. Because of the high prevalence of false results with herpes blood tests, a herpes test isn’t typically included in annual STI screening or well-woman exams.

How it’s treated: Herpes isn’t curable but there are a lot of ways to manage it and keep symptoms at bay. The CDC says antiviral medications can prevent or shorten outbreaks of genital herpes, and Planned Parenthood mentions things you can do at home, like taking a warm bath, keeping the genital area clean and dry, wearing loose clothing, and taking an OTC pain reliever like ibuprofen or acetaminophen. In some cases, your doctor may give you medicine to take every day. According to the CDC, this is called suppressive therapy and is mainly reserved for people who experience a high number of outbreaks.


HIV, or human immunodeficiency virus, is a virus that attacks the body’s immune system, and leads to AIDS, or acquired immunodeficiency syndrome. HIV is dangerous because it basically breaks down your the defense system your body has in place for fighting infection. HIV is transmitted through oral, anal, or vaginal sex, and can be passed from a mom to her baby during delivery.

What the symptoms are: Part of what makes HIV so dangerous is that most people who have it experience zero symptoms for years — sometimes as long as 10 years — and don’t realize they have it. According to Planned Parenthood, people with HIV might feel feverish, achy, and sick in the first 2-4 weeks of becoming infected because there’s a lot of the virus in your system at that stage. Those symptoms typically only last a week and then most people don’t experience symptoms again for years. Even if you’re experiencing zero symptoms, you can still give HIV to other people — another reason why protection and testing are so important.

When you should be tested: The CDC recommends everyone between the ages of 13 and 64 should be tested at least once as part of a regular health checkup. But you should also be tested more frequently if: You’re a man who has sex with other men (considered to be higher risk by doctors), have had sex with an HIV-positive partner, have had more than one new partner since your most recent HIV test, or been diagnosed with another STI (some STIs like chlamydia and herpes increase your risk for getting HIV). Planned Parenthood says it usually takes about three months for your body to produce enough antibodies to show a positive HIV blood test. The time between getting infected and testing positive is called the “window period,” and it’s also the time you’re most likely to give HIV to other people. Your doctor will work with you to discuss re-testing. It’s also worth noting that anonymous or confidential tests are available in most states.

How it’s treated: There currently is not a cure for HIV. But there are more and more medications available to treat the symptoms and slow down the virus’s progress. Antiretroviral therapy, a combination of medicines that lower the amount of HIV in your blood, is used to help people with HIV/AIDS live long, healthy lives. Other medications, like PrEP, can be taken by people who are considered high-risk for becoming infected avoid the virus.


You probably know HPV, or human papillomavrius, by a round of shots you had growing up, or from Hannah Horvath in Girls. HPV is a group of more than 100 viruses that comprise the most common STI. According to Planned Parenthood, almost every sexually active person gets HPV at some point in their lives. It’s usually harmless and goes away on its own, but some strains of HPV are known to cause cervical cancer or genital warts.

What the symptoms are: Two types — HPV 6 and 11 — cause most cases of genital warts. These warts are skin-colored or whitish bumps that appear around your genitals or anus. They’re completely treatable and not very harmful. At least a dozen types of HPV can lead to cancer, and HPV 16 and 18 lead to the majority of cancer cases and are considered high-risk HPV. Most people with high-risk HPV never show any symptoms until they’re experiencing serious health problems, which is why regular testing and prevention measures are so important.

When you should be tested: HPV can be spotted during a Pap test, which detects abnormal cells in the cervix that may be caused by HPV. The current recommendation for pap smears in women between the ages of 21 and 65 is every three to five years. Pap smears, though, aren’t a direct test for HPV — there currently isn’t a true “HPV test.” Again, this is why preventative measures (like condom usage and the HPV vaccine) are so important. And, by the way, men can get the HPV vaccine, too.

How it’s treated: Most HPV infections go away on their own and you’ll never even know you had it. Genital warts go away on their own, but sometimes need to be removed by a physician if they stick around or get larger. There isn’t otherwise a cure for HPV.


Syphilis is a common bacterial infection that causes sores on your genitals, and can have serious health consequences if it’s left untreated. The good news is that it’s easily curable if it’s detected and treated early — left untreated, it can cause brain damage, paralysis, and blindness. The bacteria is spread by skin-to-skin contact with someone who has it, and is most commonly spread through vaginal and anal sex.

What the symptoms are: According to Planned Parenthood, symptoms are hard to notice and most people don’t realize they have it. It’s also a confusing infection because there are several stages and they can overlap. The primary stage is when a syphilis sore (called a chancre) appears — it’s usually a firm, found, painless sore and often there’s only one. Chancres show up on your genitals or anus, but can also hide inside the vagina, under foreskin, inside the rectum, or other places that you can’t really see. These sores usually show up between three weeks and three months of getting an infection. The secondary stage typically includes rashes on the palms of the hands and soles of the feet, and might also cause flu-like symptoms like fever and swollen glands. The rash might last for two to six weeks at a time and can come and go for two years. The late stage can bring tumors, blindness, and paralysis and cause damage to the nervous system. In some cases, it can be fatal.

When you should be tested: Because syphilis is easily curable in its early stages — before any damage is really done — you should be tested if you notice a sore near your genitals or are showing any other symptoms, like the rash. You should also be tested if you had unprotected sex or sex with someone who has syphilis. Otherwise, if you’re sexually active, you should be tested once a year.

How it’s treated: Infections are easily cured with antibiotics (usually penicillin) prescribed by a clinician. Any sexual partners you have will need to be treated with you, so you don’t pass the infection back and forth to each other or spread it to anyone else.


Trichomoniasis, or trich, is caused by a parasite that spreads very easily during sex and is carried in sexual fluids (like semen, vaginal fluids, and even pre-ejaculate). It’s responsible for most of the cases of vaginitis, or an irritation of the vagina and vulva. It’s usually spread through vaginal sex, vulva-to-vulva contact, and sharing sex toys.

What the symptoms are: According to Planned Parenthood, seven out of 10 people with trich show now signs of infection at all. Symptoms are often so mild they aren’t detectable, or are easily confused with another infection (like a UTI or yeast infection). If you do get symptoms, they usually show up within three days to a month after becoming infected. While people of any gender can get trich, it usually shows up as vaginitis symptoms, which include: green, yellow, gray or bad-smelling discharge; blood in the vaginal discharge; itching and irritation around the vagina; and pain during sex. Other symptoms can include painful urination and the urge to pee often (hence the confusion for a UTI).

When you should be tested: If you’re having irritation, odd discharge, painful peeing, or any of the other symptoms, you should be tested. You should also be tested if you’ve had sex with someone who has trich. Tests are done with a cotton swab of the penis or vagina to check for parasites.

How it’s treated: Trich is easily cured with antibiotics, and any sexual partners you have will also need to be treated. Usually it’s only one dose of medicine.

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