And although many people who have an STI are asymptomatic, being aware of what's normal for your own body (and what's not) can help you identify if anything is wrong.
Here are some potential signs that show something could be up with your sexual health:
Lumps and bumps around your genitals
Discovering a bump or a lump on your scrotum is common and in most cases, it's not a sign of anything serious. Ingrown hairs, for instance, are common, and can cause lumps and bumps around the genitals - especially if you shave the area and have sensitive skin. However, they can also be an indicator of an infection, such as genital warts. Sue Burchill, Head of Nursing for the sexual health charity Brook says:
"Genital warts are caused by the human papillomavirus (HPV) and are small growths or bumps that appear on or around the genital or anal area. They are usually painless but look unpleasant and this can be distressing. You don't need to have penetrative sex to pass on genital warts, but they can be passed on during vaginal or anal sex, or by sharing sex toys. If you're at all concerned, get checked out as soon as possible."
Pain or burning when you pee
Lots of people notice something isn't quite right with their sexual health when they experience pain, burning or stinging whilst urinating. Most commonly this may be due to an infection of the urinary tract, which isn't an STI but can be caused by one.
According to Sue, pain or burning when you pee can actually be a symptom of several STIs, including chlamydia, gonorrhoea and trichomoniasis. If you're experiencing this, speak to your doctor because if it isn't an STI, it may still need treatment.
Discharge is often your body's way of signalling to you that something isn't quite right.
"If you notice discharge from the penis or rectum that is unusual for you, it could be an STI," says Sue. "Often a discharge that is an unusual green or yellow may be down to gonorrhoea. Whilst with trichomoniasis, you may experience a frothy, white discharge. If it's odourless, thick, white, white and a bit like cottage cheese, it's likely to be a yeast infection, or thrush."
Any kind of pain
Some STIs may cause symptoms such as pain or an unusual discomfort. "Pain can be your body's way of telling you that something is wrong, or part of you needs some care and attention," explains Sue.
If you feel pain or swelling in the testicles, this could be an indication of chlamydia, gonorrhoea or trichomoniasis, so get it checked out and don't ignore it.
Although it's really common, if you're finding sex painful, don't ignore it. According to Sue, whether it's your first time or not, sex shouldn't be painful. "Pain or bleeding during sex or after sex could be an indication of chlamydia or trichomoniasis," she says.
An eye infection
In some STIs, such as chlamydia and gonorrhoea, it's possible to transfer infected semen or vaginal fluid to the eye where it can cause an eye infection, says Bekki Burbidge, Deputy Chief Executive of the sexual health charity FPA.
"Something people often don't realise, or aren't sure about, is that you can get and pass on STIs from oral sex, so unless you know for certain that a partner doesn't have an STI, then use a condom or dam to cover the genitals or anus during oral sex."
No symptoms at all
It's very common to have an STI, but not notice any signs or symptoms. This may be due to the symptoms being mild, or you may have symptoms without realising, warns Bekki.
"Chlamydia is one of the most commonly diagnosed STIs, but one in two men with chlamydia won't have any obvious signs or symptoms, or will have symptoms so mild they're not noticed," she says. "Genital herpes is also common and many people have the herpes virus without ever knowing it. Around one in 10 men with genital gonorrhoea won't have signs or symptoms."
You can't tell whether someone has an STI just by looking at them, so if you've had unprotected sex with a new partner or someone whose STI status you're not sure of, then it's time to get tested.
If you notice anything unusual or something doesn't feel quite right, it's important to visit your GP or sexual health professional for an examination. Find out more at healthdirect.gov.au
This article originally appeared on Men's Health US.