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Yoxly Awesome Contributors

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Medically Reviewed by:

Dr Danae Maragouthakis

Sexually transmitted infections (STIs) are caused by either bacteria, viruses, or parasites and are passed between people through different types of sexual contact. This can include anything from kissing, to vaginal sex, to sharing sex toys. The different ways STIs are transmitted can get a little confusing. Many people aren’t aware of how easy it is to contract one.

Mostly, we are taught the basics about STIs at school and then they are never spoken of again. Apart from maybe during the odd trip to the doctor, or in conversations amongst our closest friends. As such, many of us will enter adulthood and not have much knowledge of how STIs can be transmitted.

In this article, we will arm you with all the knowledge you need about the transmission of STIs, so that you can take control of your sex life with confidence and reduce your risk of infections.

Common Examples of STIs

There are more than 30 different types of infections that are transmitted through sexual contact. Some show no symptoms and may exist without the person knowing. Whereas others show symptoms, such as abnormal discharge, a burning sensation when urinating, genital ulcers and abdominal pain.

Some of the most common STIs include:

Not only can STIs make you feel generally under the weather, but some can have more serious impacts on your sexual and reproductive health. These include infertility, cancers, pregnancy complications and an increased risk of contracting other STIs, including HIV.

However, as scary as this may sound, most of these complications arise as a result of long-term infections that remain untreated, or undiagnosed. Generally, frequent STI checks and practising safe sex can help prevent the long-term impacts on your health. 

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Transmission of STIs

Infections may pass between individuals via blood, semen, vaginal secretions and any other bodily fluids. Many people are not aware of the numerous ways STIs can be transmitted - it’s not just through penetrative sex! The mode of transmission is dependent on whether the infection is caused by bacteria, a virus, or a parasite.


Herpes is one of the few STIs that can be readily passed on through kissing. It is caused by an infection from the herpes simplex virus (HSV), which often produces cold sores or blisters around the mouth or genital areas.

Kissing someone with an active sore around their mouth can spread oral herpes. This is because the virus is present in saliva and the cold sore itself. Equally, performing oral sex with an active cold sore can transmit the infection to the genital area, and vice versa.

Once you have contracted the HSV virus, you will have it for the rest of your life. Although some people may never develop symptoms, or have very few outbreaks. If symptoms aren’t present, herpes is much less contagious, but can still be transmitted.

Contracting STIs through kissing is a common concern for many, particularly HIV, syphilis and hepatitis. However, you’ll be pleased to know that these STIs are highly unlikely to get passed on this way. 

Oral Sex

While the risk of contracting STIs from oral sex is lower than vaginal or anal sex, it can still transmit a number of different infections through saliva, sores, or genital fluids. Generally, if you are the receiver of oral sex, the risks are reduced as you are less likely to be exposed to genital fluids.

Oral sex with an infected partner can lead to infections in the mouth, throat, genitals, or rectum. STIs that are most commonly passed on through this type of sexual activity include herpes, syphilis, gonorrhoea and chlamydia.

The good news is there are ways to make oral sex safer! Barrier methods like condoms and dental dams can reduce the risk of transmitting infection. You should also discuss your and your partner’s sexual history and previous risks and consider having an STI test prior to engaging in oral sex.

Find out more about how to have safe oral sex.

Vaginal Sex

This is perhaps the most obvious one of all, but is still worth mentioning. Having unprotected vaginal sex with an infected person can expose you to all types of STIs. Many are symptomless and you may not even realise you are infected. It is always a good idea to get tested before each new sexual partner, to avoid the infection spreading.

Anal sex

Anal sex carries a higher risk of passing on infections than unprotected vaginal sex. This is because the anus lacks a natural lubricant and has thinner tissues, which increases the risk of tearing. Tears can allow bacteria and viruses to directly enter the bloodstream.

According to the Centers for Disease Control and Prevention (CDC), anal sex is the highest-risk form of sex for HIV transmission, particularly for the receptive partner. As such, men who engage in frequent anal sex are advised to always get tested before a new sexual partner.

Sharing Toothbrushes, Razors or Needles

STIs that are transmitted through blood can be passed on by sharing things like toothbrushes, razors, needles, or any other objects that may cause cuts or bleeding. These include HIV and hepatitis B and C. To be on the safe side, avoid sharing these objects - always bring your own toothbrush with you if you are spending the night with a new partner! Or forgo the fresh breath!

Contaminated Food

Hepatitis A is a viral infection that is often spread through contaminated food or water. The virus is found in the faeces of infected people and can be passed on during anal sex, through direct contact with infected faeces or via contaminated food or water. This is much more commonly seen in developing countries with poor sanitation and untreated water.

Skin-to-Skin Contact

The HPV virus can often be passed on without a person’s knowledge, as it is often symptomless. However, some strains can cause genital warts - soft growths that appear on the genitals - which can be transmitted through direct physical contact with the skin. According to the Centers for Disease Control and Prevention (CDC), HPV is the most common of all STIs.

Similarly, syphilis can be spread through direct contact with a sore on the skin. These often develop around the mouth, penis, vagina and anus, but can show anywhere on the body. A common myth is that you can contract syphilis by sharing a toilet with a person who has the infection. This is not true! The bacteria that cause syphilis cannot live for long outside the body.

The HSV virus (genital herpes) can also be passed by skin-to-skin contact. Transmission is more likely where a sore is present.

Sharing Sex Toys

Unwashed sex toys can also harbour bacteria and viruses that cause STIs. Sharing uncleaned sex toys with multiple people can therefore pass on STIs such as chlamydia, gonorrhoea, herpes, HPV and trichomonas. Always practice good sex hygiene and clean your sex toys after use!


That’s a lot of information to take in, we know. So, to quickly recap:

STIs are caused by viruses, bacteria, or parasites. They can be passed on through sexual or physical contact, but how they are transmitted depends on the type of infection. Some can be passed on much more easily than others, through kissing, or skin-to-skin contact. While others are only transmitted through bodily fluids or blood exchanged during anal or vaginal sex. Some blood-borne infections can also be passed on by sharing things like needles.

To reduce your risk of contracting an infection, it’s a good idea to do your homework on all the different STIs and how they are transmitted. And don’t forget to get regular STI checkups before every new sexual partner! Use our at-home testing kits to streamline the process and cut out the embarrassment.


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Yoxly's Awesome Contributors (YACs) are a diverse group of individuals who are passionate about public health, and committed to furthering our mission. Yoxly provides a platform where a variety of sexual health topics (some more awkward than others!) can be explored, in an informative and non-judgmental way. If you'd like to become one of Yoxly's Awesome Contributors, contact us!