17th March, 20214 min read

What’s the difference between an STI and an STD? STI questions answered

Medical reviewer:
Dr Ann Nainan
Dr Ann Nainan
Ana Mosciuk
Ana Mosciuk
Last reviewed: 15/03/2021
Medically reviewed

All of Healthily's articles undergo medical safety checks to verify that the information is medically safe. View more details in our safety page, or read our editorial policy.

According to the World Health Organization, more than 1 million people worldwide are infected with sexually transmitted infections (STIs) every day.

Knowing the facts about STIs can stop you from getting infected – and help you know when you might need to see a doctor or get treatment.

Not sure your STI knowledge is up to scratch? These frequently asked questions are a good place to brush up.

What’s the difference between an STI and an STD?

Both terms are used interchangeably, but they’re not the same thing.

An STI is an infection – from a virus, bacteria or parasite – that passes from 1 person to another through sexual contact. You can pass on or get an STI through vaginal, anal or oral sex.

Not every STI develops into a disease with signs and symptoms – if it does, it’s considered a sexually transmitted disease (STD). Think of it this way: infection happens first and is sometimes followed by disease.

Can I always tell if I have an STI?

No. In fact, many people don’t get symptoms, so it’s important to get tested if you think you might have an STI.

Depending on the STI, symptoms can appear within a few days or weeks. In some cases, they don’t appear until months or years after infection.

cucumber in wrapper representing a penis in a condom to protect from STIs

When should I see a doctor?

If you have any of these symptoms, visit your doctor:

  • pain or irritation when you pee
  • itchy, burning or tingling vagina or penis
  • blisters, sores, spots or lumps around your vagina, penis or anus
  • tiny white spots or black powder in your underwear
  • unusual or smelly discharge from your vagina or penis
  • pain during sex
  • lower tummy pain
  • bleeding after sex
  • bleeding between periods

Does an STI test hurt?

Some tests may feel uncomfortable briefly – some won’t hurt at all.

Depending on the type of test you need, you may be asked for:

  • a blood sample (usually for HIV and syphilis tests)
  • a pee sample (for STIs like chlamydia and gonorrhea)
  • swabs from the urethra (where pee comes out)
  • swabs from the throat, vagina, penis or anus

Can I do an STI test at home?

Yes, for some STIs – like chlamydia, gonorrhoea and HIV – you can use home testing kits. Some kits are available online, but it’s better to speak to a health professional, like a pharmacist, to get advice on which kit is best and how to use it.

Do STIs go away on their own?

No. Only STIs caused by the human papillomavirus (HPV) are cleared by the body for most people, without causing any problems. However, for some, certain types of HPV can lead to genital warts or cervical cancer.

Leaving STIs untreated can lead to long-term health and fertility problems, so it’s worth getting checked out by a doctor as soon as you think you might have an STI.

Are STIs treated with antibiotics?

These STIs caused by bacteria are treated with antibiotics:

  • chlamydia
  • gonorrhoea
  • syphilis

Trichomoniasis – an STI caused by a parasite – is also treated with antibiotics.

Can all STIs be cured?

While some STIs can be cured with antibiotics, there is no complete cure for these viral infections – though antiviral medications can help treat symptoms:

Safe and effective vaccines are available for HPV and hepatitis B.

Want to check STI symptoms?

The Healthily app can help you identify STI symptoms and let you know when you need to get medical treatment – once you've downloaded the app, just start chatting to DOT about your symptoms (assessments are anonymous).

Key points

  • an STI is an infection that spreads through vaginal, anal or oral sex
  • if an STI develops into a disease with symptoms, it’s called an STD
  • you can’t always tell if you have an STI, as many people don’t have symptoms
  • it’s important to see your doctor as soon as you think you might have an STI
  • you can test for some STIs yourself, with home testing kits
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