At a glance
- A sexually transmitted infection (STI) is an infection spread between people during sex or close sexual contact.
- STIs are common in teenagers and young adults who are sexually active.
- Using condoms or other barrier protection is the best way to avoid STIs.
- You might not have symptoms if you have an STI.
- If you are sexually active, you should get tested for STIs regularly.
- STIs can have serious long-term health effects if you don’t treat them.
What is a sexually transmitted infection (STI)?
A sexually transmitted infection (STI) is an infection spread from one person to another during sex or close sexual contact. All types of sex and sexual activity with intimate body parts can pass on STIs – not just penetrative sex.
STIs are more common than you might think. You are more likely to get an STI if you have:
- sex without using a condom or another form of barrier protection
- multiple sexual partners
- a new sexual partner.
It’s also possible to have more than one STI at the same time.
The best way to avoid STIs is to use barrier protection like condoms. Other contraceptives, like the pill, don't protect you
from STIs; they only prevent pregnancy.
Most common STIs in teens
Chlamydia
What is it?
Chlamydia is the most common STI in young people. It’s an infection caused by the bacterium Chlamydia trachomatis that can infect the cervix (connects the vagina to the uterus), urethra (tube that carries urine), anus, throat, and sometimes eyes.
Chlamydia is easy to treat with a short course of antibiotics. If you don't treat it, you could have long-term problems like pain and trouble having babies in the future.
What are the symptoms?
Lots of people with chlamydia don't have any symptoms. This is one reason why it’s important to get regular STI checks if you are sexually active.
If you do have symptoms, you might get:
- discharge from the penis, vagina or anus
- pain in the pelvis or lower belly
- a stinging or burning feeling when peeing
- pain during sex
- bleeding from vagina after sex.
Gonorrhoea
What is it?
Gonorrhoea is an infection caused by a bacterium called Neisseria gonorrhoeae. It lives in the genital fluid of infected people, so you can get this STI during penetrative sex as well as by sharing sex toys or touching the genital skin of someone
infected. Gonorrhoea can infect the cervix, urethra, anus, throat and eyes. Sometimes, it spreads through the body, causing fevers and joint infections. You can treat gonorrhoea with antibiotics.
What are the symptoms?
Like chlamydia, you might not get any gonorrhoea symptoms.
If you have symptoms, you might get:
- discharge from the penis, vagina or anus
- pain in the penis, vagina or anus
- a stinging or burning feeling when peeing
- pain during sex
- bleeding after sex
- pain in the pelvis or lower belly
- a sore throat.
Staying safe from STIs
The best way to avoid catching STIs is by using barrier protection every time you are sexually active. External condoms are the most common barrier protection for sex with a penis, but there are also:
- internal condoms
- dental dams (a thin, square sheet placed over flatter areas like the vagina and anus during oral sex).
If you are sexually active, you should see your local doctor (general practitioner or ‘GP’) regularly for STI checks. For most people, it's best to get tested every six to 12 months. If you test positive for infections, it's very important to take any
treatments your GP prescribes. Always let your sexual partner(s) know if you have an STI.
Some STIs can spread through contact with other bodily fluids, like blood. So, make sure you are careful when doing anything with bodily fluids like tattoos, piercings and injections. All tools should be clean and free of germs (sterilised) before use,
and needles should be new.
HPV vaccine
Human papillomavirus (HPV) is a virus spread by skin-to-skin contact. It can cause genital warts and cancers. Thankfully, there is a vaccine that can prevent most types of HPV. Teenagers in Australia can get the HPV vaccine for free at school in year
seven as part of the National Immunisation Program. You don’t need to be sexually active to get the vaccine.
If you missed the HPV vaccine at school or moved to Australia from another country, it's not too late. Doctor’s clinics and some pharmacies will give you the HPV vaccine for free up to age 25 – they might just charge a small admin fee.
How do doctors test for STIs?
Different kinds of tests check for STIs. Some test types are:
- Swabs: A swab collects a sample of cells to test for STIs. If you don't have any symptoms, you can usually do the swab sample yourself. A doctor or other health worker will explain how to do this. If you have symptoms, the doctor will do the
swab sample.
- Urine tests: A urine (pee) test can also check for common STIs like chlamydia and gonorrhoea – especially if you can't do a swab test.
- Blood tests: A blood test can check for some STIs that a urine test or swab won't find, like HIV and syphilis.
I think I have an STI. What should I do?
If you think you have an STI, you should:
- see your GP or another doctor as soon as possible
- stop having sex until you have seen a doctor.
Many major cities in Australia have sexual health clinics where you can see a doctor, nurse, or other trained health worker without an appointment. You don't usually need to be a regular patient.
If tests confirm you have an STI, your GP (or other health worker) will:
- Prescribe any treatments you need, like antibiotics.
- Give you advice on how long to wait before you have sex again.
- Organise a follow-up test to make sure the treatment worked (if needed).
- Suggest ways to tell your sexual partner(s) you have an STI so that they can get tested, too. This is called 'contact tracing.' It’s an important step in stopping the spread of STIs. You can let your partner(s) know yourself if you are comfortable,
or use a contact service without your details to stay anonymous.
Many STIs are 'notifiable infections’ in Australia, including chlamydia and gonorrhoea. This means the Australian Government Department of Health collects data on how many cases of these STIs there are every year. Your GP must tell the Department of Health
if you test positive for some STIs, but they won't share your full name or other personal information. No one else can see these details, either.
Things you might be wondering
Can you get an STI if you haven’t had penetrative sex?
STIs usually spread through sex. However, some STIs can also spread through kissing, genital skin contact, sex toys and bodily fluids like blood. So, it's possible to catch some STIs from anything that involves sharing these fluids, like unclean
piercing tools. The bacteria and viruses that cause STIs cannot survive for long outside the human body. Despite what you might have heard, you won't catch an STI from a dirty toilet seat.
Are cold sores a type of STI?
The virus that causes cold sores is in the same family as the genital herpes virus, also known as Herpes Simplex Virus (HSV). It spreads through kissing, sex, and contact with intimate body parts. Some people don't get any symptoms, but others
might have painful blisters, ulcers or sores, pain and swelling in the genital area, and a rash or small cracks in the skin. Herpes is very common, and it’s nothing to feel ashamed about. Although there is no cure for herpes, people with the
virus can still have relationships and live normal lives. Symptoms can come and go; you might get cold sores if you are sick, tired or have low immunity. These are called ‘outbreaks.’ There are treatments to help outbreaks happen less over
time, and might even stop them from coming back again. Because the virus stays in your body even if you don’t have symptoms, it’s a good idea to use barriers like condoms or dental dams during sex.
Is a urinary tract infection (UTI) an STI?
A urinary tract infection (UTI) is not an STI, but sex can increase the risk of getting a UTI. This is because bacteria cause a UTI,
and sex introduces different kinds of bacteria to the genital area. Getting a UTI doesn’t mean the person you had sex with is dirty. Everyone has bacteria that naturally live on the skin around their genital area. Having sex just makes it
more likely that these bacteria get into your urinary tract. Some symptoms of a UTI are the same as many STIs, too, like a burning feeling while peeing.
What are some other STIs I should know about?
There are many other STIs that aren't in this fact sheet, such as HIV, syphilis and hepatitis. Some people are at higher risk of HIV, such as men who have sex with men. There are medicines to help prevent HIV, such as PrEP and PEP, that you can use before or right after you might have been exposed to HIV.
What happens if I don’t treat my STI?
Many STIs can have harmful long-term health effects if you don’t treat them. Some possible health problems of untreated STIs are pain, a higher risk of some cancers and the inability to have babies in future (infertility). The good news is that
most STIs are treatable. That’s why you should test for STIs regularly, take any medicines prescribed if you have an STI, and tell your partner (or partners) to get tested and treated, too.
Do I have to tell my parents if I have an STI?
As a teenager, you have a right to private and confidential health care. This privacy means
you (and your GP or other health worker) don't usually need to tell your parents if you have an STI. In most cases, it's best to tell your parents so they can help you get the care you need. Your GP might need to tell your parents or someone
else if you are not safe. For example, if you are under 16 years old and you have had sex with someone who is more than two years older than you.
Helpful links
Developed by The Royal Children’s Hospital (RCH); medical review by the Adolescent Medicine department, with input from the Gynaecology and Infectious Diseases departments. Created with advice from the RCH Health Literacy Youth Advisory Committee.
Reviewed August 2025
Speak with a doctor for up-to-date and personalised medical advice.