What is the difference between an STI and an STD?

Liz Wood Alphabiolabs

By Liz Wood, Health Testing Specialist at at AlphaBiolabs
Last reviewed: 16/12/2022

In this article, we discuss the difference between sexually transmitted infections (STIs) and sexually transmitted diseases (STDs), common symptoms, and how you can keep your sexual health in check with regular testing.
Table of contents
  • What is a sexually transmitted infection (STI)?
  • What is a sexually transmitted disease (STD)?
  • What is the difference between an STI and an STD?
  • What is the difference between a disease and an infection?
  • What are the symptoms of STIs vs STDs?
  • How can I get tested for STIs/STDs?

What is a sexually transmitted infection (STI)?

A sexually transmitted infection (STI) – sometimes referred to as a sexually transmitted disease (STD) – is an infection that is most commonly passed on to other people during sexual activity.

Many STIs are spread via bodily fluids such as semen or vaginal fluids but can also be passed on during skin-to-skin contact (e.g. herpes).

You can catch STIs from vaginal, anal and oral sex, sexual touching (e.g. touching genitals), and by sharing sex toys.

Some STIs, such as HIV, syphilis, and hepatitis, can also be spread via blood.

What is a sexually transmitted disease (STD)?

A sexually transmitted disease (STD) – sometimes referred to as a sexually transmitted infection (STI) – is an umbrella term for a group of infections that are most commonly passed on to other people during sexual activity.

Many STDs are spread through infected bodily fluids such as vaginal or seminal fluids during sexual activity (e.g. vaginal, anal, oral sex).

However certain types can also be spread via skin-to-skin contact (e.g. herpes) and blood (HIV).

What is the difference between an STI and an STD?

Both ‘STI’ and ‘STD’ are umbrella terms that are used to refer to infections that are commonly spread via sexual activity.

These terms can be (and often are) used interchangeably to describe infections caused by bacteria, viruses or parasites that are spread via bodily fluids (e.g. semen, vaginal fluids, blood) or during skin-to-skin contact with an infected person.

Historically, ‘STD’ was the term that was most used to refer to any infections that could be passed on during sexual activity.

However, this has become less popular over time, with more people, including healthcare providers, now using the term ‘STI’ to refer to these infections, possibly due to the negative connotations that are sometimes associated with the word ‘disease.’

What is the difference between a disease and an infection?

An infection can be caused by microorganisms such as bacteria and viruses, or larger organisms like parasites.

Many infections are contagious, meaning that they can be easily passed on to other people through a variety of means including touching, coughing, sneezing, sexual contact etc.

A disease can be contagious or non-contagious. Diseases can be caused by infections, but can also be caused by other things, such as lifestyle, environmental factors, injury, and hereditary (inherited/genetic) factors.

Many people who have an infection – such as a sexually transmitted infection (STI) for example – may not display any symptoms for days, weeks, months or even years, depending on the type of infection they have.

In those who experience symptoms, the body will trigger an immune response to try and combat the infection. This can usually be seen via external symptoms – for example, a person with symptoms of gonorrhoea may experience abnormal discharge, painful urination and itching or burning genitals.

If a person has an infection but no symptoms, and the infection remains untreated, it may remain in their body for a long period of time.

Depending on the type of infection they have, the infection may develop into the disease stage over time, leading to more serious long-term health complications.

When talking about sexual health, ‘STIs’ and ‘STDs’ are umbrella terms that are used interchangeably to refer to any infections that can be passed on during sexual activity.

What are the symptoms of STIs vs STDs?

The terms ‘STI’ and ‘STD’ are used interchangeably to refer to infections that are commonly passed on to other people during sexual activity, either via bodily fluids (e.g. semen, vaginal fluid, blood), or skin-to-skin contact.

This means that there is no fundamental difference between the symptoms associated with STIs versus STDs. However, symptoms will vary depending on the type of infection a person has (e.g. chlamydia vs herpes), when they first became infected, and whether they have had the infection before, among other factors.

Some common symptoms that have been linked to several STIs/STDs include:

  • A burning sensation when urinating
  • Unusual and/or strong-smelling discharge from the penis or vagina
  • Burning and itching around the genitals
  • Pain during sex
  • Unusual bleeding from the vagina

However, it’s important to remember that many people with an STI/STD will not have any symptoms at all. This is known as being asymptomatic.

If a person is asymptomatic, this greatly increases the risk of infections being passed on to other people during sexual activity, as they may not know they have an infection unless they take an STI test.

If you are experiencing symptoms that are causing severe pain and discomfort, or that require a face-to-face examination, we advise you to contact your GP or local sexual health clinic as soon as possible.

For more information on STI symptoms, visit www.sexwise.org.uk.

How can I get tested for STIs/STDs?

Regular STI testing can help you keep your sexual health in check and ensure any infections are detected early, so that you can seek the correct treatment via your GP or local sexual health clinic.

Many people with an STI/STD do not display any symptoms (are asymptomatic). This makes regular testing even more important for reducing the spread of infections.

AlphaBiolabs offers a range of home STI tests for this purpose, starting from just £29.

Depending on which test you choose, you will need to provide a urine sample, vaginal swab sample, lesion swab sample or a finger-prick blood sample for analysis at our UK laboratory.

Our test kits have been designed to enable you to collect your own sample quickly and discreetly at home.

However, if you are experiencing symptoms that are causing severe pain and discomfort, or that require a face-to-face examination, we advise you to contact your GP or local sexual health clinic as soon as possible.

Please note, you must be at least 16 years of age to purchase a home STI test kit from AlphaBiolabs.

Order an STI test kit

At-home STI testing you can trust, from just £29.

Liz Wood

Liz Wood

Health Testing Specialist at AlphaBiolabs

Liz joined AlphaBiolabs in 2021, where she holds the role of Health Testing Specialist.

As well as overseeing a range of health tests, she is also the lead on several validation projects for the company’s latest health test offerings.

During her time at AlphaBiolabs, Liz has played an active role in the validation of the company’s Genetic Lactose Intolerance Test and Genetic Coeliac Disease Test.

An advocate for preventative healthcare, Liz’s main scientific interests centre around human disease and reproductive health. Her qualifications include a BSc in Biology and an MSc in Biology of Health and Disease.

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