The Most Common STIs in Teens – Symptoms

The Most Common STIs in Teens – Symptoms, Complications, and Risks of Not Getting Treated

Being a sexually active teenager means it’s important to know about sexually transmitted infections (STIs). STIs (also called STDs) are infections spread through sexual contact, and teens and young adults have some of the highest rates of STIs worldwide. In this article, we’ll break down a few of the most common STIs that affect teenagers, what symptoms to watch for, the complications they can cause, and why getting prompt treatment matters. Don’t worry – we’ll keep it straightforward and not too formal, so it’s easy to understand.

Higher-Risk vs Lower-Risk Sexual Behaviours

What they are: Chlamydia and gonorrhea are bacterial STIs that are very common in people under 25. In fact, gonorrhea is “very common, especially among young people ages 15–24” according to the CDC[1]. Both infections are passed on through vaginal, anal, or oral sex.

Symptoms: Often, no symptoms at all! Both chlamydia and gonorrhea frequently do not cause noticeable symptoms, especially in young women[2][3]. This means a teen could have the infection and not know it. When symptoms do occur, they can be mild or mimic other common issues (like a urinary tract infection). Some possible signs include:

Pain or burning when you pee: This can happen in anyone with chlamydia or gonorrhea (for both guys and girls)[4][5]. It might just feel like a UTI.
Unusual discharge: Girls might notice an abnormal vaginal discharge, and boys might see discharge (white, yellow, or green) from the penis[6][7].
Bleeding or pain: Girls might have bleeding between periods or pain in the lower belly; guys might have soreness or swelling in the testicles (though this is less common)[5][8].
Rectal symptoms: If either infection spreads to the rectum (for example, from anal sex), it could cause rectal pain, discharge, or bleeding in anyone[9][10].

Remember, most teens with chlamydia or gonorrhea feel totally fine – which is why regular STI testing is important if you’re sexually active. The good news is that both chlamydia and gonorrhea are curable with antibiotics (usually a simple prescription). But untreated infections can lead to serious problems.

Complications if untreated: When not treated, these bacterial infections can move deeper into the reproductive tract and cause pelvic inflammatory disease (PID) in people with a uterus[11][12]. PID is an infection of the female reproductive organs that can result in:

Scar tissue and blocked fallopian tubes (the tubes that carry eggs)[11][13]
Ectopic pregnancy, meaning a pregnancy outside the womb, which is dangerous[11][13]
Infertility, or trouble having children in the future[14][15]
Chronic pelvic pain that can last a long time[16][13]

Boys don’t often face such severe long-term issues, but untreated chlamydia or gonorrhea can lead to a painful infection in the testicles (epididymitis) and may cause infertility in rare cases[17][18]. Another risk for everyone is that having chlamydia or gonorrhea makes it easier to get or spread HIV if exposed, due to the inflammation these STIs cause[19][20]. Also, if a pregnant teen has one of these infections and it’s not treated, she could pass it to her baby during childbirth, leading to eye infections or other serious problems in the newborn. In short, not treating chlamydia or gonorrhea can really mess with your health down the road – from fertility problems to higher HIV risk – even though you might feel perfectly okay right now.

(References: [1], [2])

HPV and Genital Warts

What it is: HPV stands for human papillomavirus. It’s actually a whole group of viruses, and it is the most common STI in the world[21]. There are many types of HPV. Some types cause genital warts, while other types can lead to cancer (most famously cervical cancer, but also throat, anal, or penile cancers). HPV spreads through skin-to-skin sexual contact. Because it’s so common, most sexually active people will catch HPV at some point – but often it never causes any issues.

Symptoms: Often, none. Most people with HPV don’t have any symptoms and may clear the virus on their own without ever knowing they had it[22]. In about 9 out of 10 cases, the immune system fights off HPV within two years[23]. However, when HPV doesn’t go away, it can cause visible genital warts or even cancer years later[23].

Genital warts: These are usually the only visible symptom of HPV. Warts appear as small bumps or groups of bumps in the genital area. They can be tiny or large, flat or raised, and sometimes look like a cauliflower in shape[24]. They’re usually painless, but can be itchy or just cosmetically bothersome. Warts might go away on their own, or stay the same, or grow – there’s no set pattern[25]. A doctor can recognize and treat genital warts easily (by freezing them, for example).

Aside from warts, you won’t be able to tell if you have HPV. There’s no routine test for HPV in teens with penises, and for those with a cervix, HPV is usually detected through abnormal Pap smear results (a screening test usually done starting at age 21).

Complications if untreated: The warts themselves generally don’t cause dangerous health problems[26] – they’re more of a nuisance and can be treated. The more serious issue is the cancer risk from certain high-risk HPV strains. If an HPV infection persists (doesn’t get cleared by your body) and it’s a type that causes cell changes, it can lead to:

Cervical cancer: a cancer of the lower part of the uterus. Almost all cases of cervical cancer are linked to untreated HPV infections. This usually takes years to develop and can be caught early with regular screening (Pap tests).
Other cancers: HPV can also cause cancers of the throat (oropharyngeal cancer), anus, penis, vulva, or vagina later in life if the infection isn’t cleared. These are also rare and usually involve high-risk HPV types.

It’s important to note that the types of HPV that cause genital warts do NOT cause cancer[27]. There are “low-risk” HPV types (like 6 and 11) that cause warts, and “high-risk” types (like 16 and 18) that cause most cancers. So having warts does not mean you’re going to get cancer – but it does tell you that you have an HPV infection. Because HPV is so common and often silent, the best protection is vaccination. The HPV vaccine is recommended for teens and can prevent infection by the most dangerous strains (it’s a huge advance – it can prevent over 90% of HPV-related cancers from ever developing[28]). Using condoms can also lower HPV transmission, though they don’t block it completely because HPV can infect areas not covered by a condom[29][30].

In summary, untreated HPV might not affect you at all – or it could eventually lead to warts or cancer, depending on the type. That’s why monitoring (for people with a cervix, through Pap smears when older) and vaccination are key.

(References: [3])

Herpes (Oral and Genital)

What it is: Herpes is caused by the herpes simplex virus. There are two main types: HSV-1 and HSV-2. HSV-1 is the one usually associated with cold sores on the mouth (oral herpes), and HSV-2 is usually associated with genital herpes. However, both types can infect the genital area or the oral area – for example, if someone with a cold sore performs oral sex, they could give their partner genital HSV-1 infection[31][32]. Herpes spreads through direct skin-to-skin contact, which includes kissing or any sexual contact. Once you catch herpes, the virus stays in your body for life (it hides in nerve cells), but it doesn’t mean you have symptoms all the time.

Symptoms: Many teens (and adults) with herpes have no idea they have it because they never notice symptoms or their symptoms are super mild[33][34]. If symptoms do appear, the classic sign is an outbreak of painful blisters or sores at the site of infection (around the mouth for oral herpes, or on the genitals for genital herpes). Here’s what can happen:

Early signs: People often feel an itching, tingling, or burning in the spot where a blister is about to form. This can be a heads-up that an outbreak is coming[35].
Blisters and sores: Fluid-filled blisters appear and then burst, leaving open sores (which can be really painful, especially for genital herpes when you pee)[36]. The sores eventually scab over and heal within a few weeks during an initial outbreak[36]. In a first-time outbreak, someone might also get flu-like feelings – fever, body aches, swollen glands[37][38].
Recurrences: After the first outbreak, the virus goes into hiding, but it can reactivate later. Recurrent outbreaks are usually shorter and less intense than the first one[39][40]. Some people only ever have one outbreak; others have them off and on. Things like stress, illness, or even sunlight (for oral herpes) can trigger outbreaks[41].

Oral herpes (cold sores) often first happens in childhood (like from a relative’s kiss) and by the time people reach their teens, a huge portion of the population has HSV-1. Globally, about 3.8 billion people under 50 (around 2/3 of that age group!) have HSV-1[42], though not everyone gets cold sores. Genital herpes is also common – worldwide about 13% of people 15–49 have HSV-2, the main cause of genital herpes[43]. So if you have it, you’re definitely not alone.

There is no cure for herpes yet. But untreated doesn’t mean the same thing here as it does for, say, chlamydia, because herpes is a virus that stays in your body. We can treat the symptoms and reduce outbreaks with antiviral medications (like acyclovir), but the virus itself isn’t killed off. So the concerns with “not treating” herpes are more about managing it and preventing spread:

Complications if untreated:
Painful sores and discomfort: Without treatment, outbreaks might last longer or be more frequent. Herpes can be pretty painful during an outbreak, which can seriously affect your comfort and sex life. Treatment can help sores heal faster and suppress outbreaks.
Higher risk of HIV: Herpes can make it easier to get HIV if you’re exposed to it. The sores or even microscopic breaks in the skin help HIV enter the body more easily[44][45]. In fact, having HSV-2 roughly triples the risk of acquiring HIV if exposed (because of the immune cells HSV brings to the skin)[44]. So, untreated herpes (especially if it causes frequent sores) can increase the chance of contracting HIV or passing it on.
Spreading the virus to others: If you don’t take precautions, herpes can easily spread through sexual contact or kissing. Even when you don’t have visible sores, the virus can sometimes shed from your skin. Without any management (like daily suppressive therapy or avoiding sex during outbreaks), there’s a higher chance of passing it to partners.
Severe infections (rare): In people with weakened immune systems (say someone with uncontrolled HIV or other immune problems), untreated herpes can cause serious complications – the sores can be more severe and widespread, and in very rare cases herpes can spread to other organs like the brain (herpes encephalitis). This is not typical in a healthy teen, but it’s why we treat outbreaks aggressively in immunocompromised patients[46].
Newborn babies: One of the biggest concerns is for pregnant women with herpes. If a woman has active genital herpes during childbirth, the baby can catch it, and newborn herpes infections are extremely dangerous. Untreated herpes in pregnancy can lead to miscarriage or neonatal herpes, which can be life-threatening for the baby[47]. Fortunately, doctors usually manage this by giving antiviral meds in late pregnancy or doing a C-section if an outbreak is present to protect the baby.

Emotionally, an untreated herpes diagnosis can also cause stress or anxiety about outbreaks or disclosing to partners. But knowledge and treatment help – taking daily antiviral medication can greatly reduce outbreaks and the chance of transmission to others[39][48]. Many people with herpes still have healthy relationships and normal lives; it’s all about managing it. So, while herpes won’t wreck your fertility or organs like some other STIs, ignoring it isn’t wise because of the discomfort, the risk of HIV, and the risk to partners or babies. With treatment and precautions, herpes is a manageable condition.
(References: [4], [7])

Trichomoniasis and Other Parasitic Infections

Not all STIs are viruses or bacteria – some are caused by tiny parasites. The big one in this category that affects teens is trichomoniasis, and there are also little critters like pubic lice (aka “crabs”) and scabies mites that can be passed through sexual contact. Let’s break these down:

Trichomoniasis (“trich”): This is a common STI caused by a protozoan parasite (a one-celled organism) called Trichomonas vaginalis. It’s spread mainly through vaginal sex. Trich is super common – millions of cases occur every year. The tricky part is most people don’t know they have it. About 70% of those infected have no symptoms at all[49][50]. When symptoms do happen, they usually show up within 5 to 28 days of exposure, but can be very mild. Here are some signs:

Vaginal symptoms (in girls): itching, burning, redness, or soreness down there; discomfort or a burning feeling when peeing; and a change in discharge – it might become clear, white, yellowish, or greenish and often has a fishy odor[51][52]. The discharge from trich can be thin or frothy and might be more than usual. These symptoms can come and go.
Penile symptoms (in guys): most men don’t notice anything. Some might feel a slight irritation inside the penis, mild discharge, or a burning sensation after peeing or ejaculating[53]. It’s usually pretty subtle, so many guys have trich and never realize it unless their partner gets diagnosed.

Trichomoniasis is curable with medication (usually a single dose of a prescription antibiotic like metronidazole or tinidazole). It’s one of those STIs that can be knocked out fairly easily once you know it’s there. However, if you don’t get treated, trich can linger for months or even years in your body[54].

Complications if untreated (Trichomoniasis): Even though trich won’t cause the kind of organ damage that, say, chlamydia can, it can lead to some significant problems if ignored:

Prolonged Discomfort: Untreated trich can continue to cause annoying symptoms (itching, irritation, unpleasant discharge) that might affect your confidence or comfort during sex. It can literally make sex feel unpleasant due to the irritation[54].
Higher risk of other STIs: Trichomoniasis can cause genital inflammation, and that makes it easier to get infected with other STIs or to pass them on. For example, trich can increase the risk of acquiring or transmitting HIV[55]. Your skin and tissues are a bit more vulnerable when inflamed.
Pregnancy issues: If a pregnant teen has untreated trich, there’s a greater chance of premature birth (having the baby too early) and the baby having a low birth weight[56]. So, trich is bad news for pregnancy outcomes if not treated.
Possibility of fertility problems: Some research and health agencies note that untreated trich might contribute to infertility in women or complications like PID in rare cases[57]. This link isn’t as strong as with chlamydia or gonorrhea, but there is a concern that long-term trich infections could play a role in reproductive issues[57]. At the very least, it often co-exists with those other infections, complicating the picture.

Bottom line: trich won’t destroy your reproductive organs overnight, but leaving it untreated means you could unknowingly spread it to others and raise your risk for other infections. And since it’s so easy to cure, there’s no good reason to ignore it. If you find out you have it, make sure your sexual partners get treated too, or you might pass it back and forth.

Pubic Lice (“Crabs”): Pubic lice are tiny six-legged insects that infest coarse body hair, especially around the genital area. They are considered an STI because they spread often through sexual or close bodily contact. If someone mentions “crabs,” they’re talking about these little lice – they’re called that because under a microscope they look kind of like tiny crabs. How do you know if you have them? Intense itching in the pubic area is the big clue. You might also see tiny white-ish eggs (nits) stuck to pubic hair, or even small tan or gray lice crawling there[58]. (Ew, we know – but it’s a common issue and it doesn’t mean someone is “dirty”. It just means they had close contact with someone who had them.) Pubic lice do not transmit other diseases[59], and they’re more of a nuisance than a serious health threat. However, scratching the itchy bites can lead to secondary skin infections or sores[59]. Crabs can also live in other body hair like armpits, chest hair, or even eyebrows and eyelashes.

Treatment for pubic lice is straightforward: over-the-counter creams or shampoos (lice-killing lotion with permethrin or similar) applied to the affected areas will usually kill them[60]. You’ll also need to wash any clothes, bedding, or towels you used in hot water to kill any stray lice or eggs[61]. It’s also important to inform sexual partners so they can be checked/treated – otherwise you could pass the lice back and forth. Untreated pubic lice will continue to cause itching and can spread to others; they won’t go away on their own. But once you treat them, they’re gone.

Scabies: Scabies is another parasitic infestation caused by mites that burrow under the skin. It’s not always sexually transmitted (you can catch scabies from any prolonged skin-to-skin contact or even shared bedding), but in teens and adults it often spreads through intimate contact. Scabies causes an extremely itchy rash, often with small bumps or lines on the skin where the mites have tunneled. Common areas are between fingers, wrists, abdomen, and yes, the groin. Like pubic lice, scabies mites cause intense itching especially at night. They are treated with prescription creams that kill the mites. If you spend the night with someone who has scabies, there’s a decent chance you’ll get it too[62][63]. Untreated scabies can persist and spread to others, and the itching can drive you crazy, but treatment will cure it.

In summary, parasitic STIs like trichomoniasis, pubic lice, and scabies are all treatable or curable. If you don’t treat them, you’re in for ongoing discomfort (and in the case of trich, potential health risks like easier HIV infection or pregnancy complications). It’s nothing to be ashamed of – these infections are common, and a doctor or clinic can help you get rid of them fairly easily.

(References: [5], [6])

Sources

Authoritative health organizations provide guidance on teen sexual health and safety[9][19][16][22]. These include CDC and pediatric experts; see their recommendations on STI prevention, consent, and healthy relationships to learn more.

What Happens If STIs Go Untreated?

We’ve touched on this in each section, but it’s worth repeating: Untreated STIs can lead to serious long-term consequences, even if you feel fine now. Teenagers sometimes avoid getting checked out of fear or not noticing any problems. But ignoring an STI won’t make it go away – and it could make things worse. Here’s a quick recap of why treatment is so important:

Infertility and reproductive harm: Several common STIs (especially chlamydia and gonorrhea) can cause scarring in the reproductive organs if not treated, potentially leading to infertility (inability to have children in the future)[11][64]. In girls, untreated infections can cause pelvic inflammatory disease with blocked fallopian tubes or ectopic pregnancies, and in guys, infections can (rarely) scar the testicles or tubes, affecting sperm. Even trichomoniasis has been linked to fertility problems if left unchecked[57]. In short, not treating an STI now might mean trouble getting pregnant or having a healthy pregnancy later on.
Chronic pain and health issues: Untreated STIs can lead to chronic pelvic pain (from PID)[16][13], ongoing genital pain, or recurrent sores (in the case of herpes) that keep coming back. Syphilis (another STI not covered above) can, if untreated for years, cause damage to the heart, brain, and other organs. HIV, if not treated, will progressively destroy the immune system (leading to AIDS). These are extreme examples, but they show that STIs are not “no big deal” if you ignore them.
Higher risk of other infections: Having any untreated STI that causes inflammation makes you more susceptible to catching HIV or other STIs. For instance, untreated herpes or trichomoniasis can raise the risk of getting HIV if exposed[65][44]. Also, if you have one STI, you might have others – so not getting tested/treated means those could be lurking and causing damage too.
Cancer risks: As we discussed with HPV, an untreated high-risk HPV infection can lead to cancer down the line. Likewise, hepatitis B and C (which can be sexually transmitted) can cause liver cancer if untreated. These outcomes usually take years, but they start with an infection that wasn’t cleared or managed.
Passing it to others: An untreated STI in you means you can unintentionally spread it to your partners. For example, if you don’t know you have chlamydia, you might give it to someone else, and the cycle continues. Or if you have HIV or hepatitis and don’t get treatment, your viral load stays high, and that increases the chance of transmission. Even something like untreated syphilis in a pregnant woman can pass to her baby, causing congenital syphilis (a very serious condition for infants).
It only gets worse: Many STIs actually start with mild symptoms and then go into latent stages where you feel okay, but the bacteria or virus is quietly causing damage. Syphilis is a classic example – early on it causes a sore that goes away, but years later untreated syphilis can affect your brain and nerves. The point is, with STIs, what you don’t see can hurt you. By the time obvious symptoms or complications show up, the damage might be done.

The bottom line: If you ever find out you have an STI, or even suspect it, don’t ignore it. Most STIs are treatable – many are even curable with the right medications. And for those that aren’t curable (like herpes or HIV), we have effective treatments to manage them and keep you healthy. The sooner you address an STI, the better your outcome and the less chance of long-term problems.

STIs carry a lot less stigma and health risk when you deal with them proactively. Getting tested regularly, practicing safer sex (using condoms/dental dams, limiting partners, etc.), and getting recommended vaccines (like HPV and hepatitis B vaccines) are all ways to stay on top of your sexual health. If something seems off – say, a weird discharge, a bump, or just a gut feeling – see a healthcare provider. Many clinics and school health centers provide teen-friendly STI testing that’s confidential.

Untreated STIs can seriously affect your future, but treated STIs don’t have to. Knowledge is power: by knowing the symptoms and risks of these common infections, you’re already taking a big step toward protecting yourself and others. Stay informed, be responsible, and remember that taking care of your sexual health is an important part of taking care of you.

References

Centers for Disease Control and Prevention (CDC). (2025, January 31). About Chlamydia. Retrieved from https://www.cdc.gov/chlamydia/about/index.html
Centers for Disease Control and Prevention (CDC). (2025, January 31). About Gonorrhea. Retrieved from https://www.cdc.gov/gonorrhea/about/index.html
Centers for Disease Control and Prevention (CDC). (2025, January 31). About Genital HPV Infection. Retrieved from https://www.cdc.gov/sti/about/about-genital-hpv-infection.html
Centers for Disease Control and Prevention (CDC). (2024, February 20). About Genital Herpes. Retrieved from https://www.cdc.gov/herpes/about/index.html
Centers for Disease Control and Prevention (CDC). (2025, January 31). About Trichomoniasis. Retrieved from https://www.cdc.gov/trichomoniasis/about/index.html
Centers for Disease Control and Prevention (CDC). (2024, June 4). About Pubic “Crab” Lice. Retrieved from https://www.cdc.gov/lice/about/pubic-lice.html
World Health Organization (WHO). (2022). Herpes simplex virus – Key Facts and Overview. Retrieved from https://www.who.int/news-room/fact-sheets/detail/herpes-simplex-virus