The influenza virus is an incredibly harmful infection that causes untold millions misery when flu season comes along. For some, the flu can even be fatal.

One of the things that makes the flu a problematic disease in the context of STIs is its symptoms.

The flu shares a lot of symptoms with other infections, including many STIs. This is what makes STIs so dangerous. Many people infected with STIs mistake their symptoms for the flu or another infection, and they assume their illness will pass. But this isn’t the case.

In this blog, we’ll review the symptoms of the flu and compare them to the symptoms of various STIs. We will then try to differentiate them so that you can know for sure if you have the flu or an STI.

Flu symptoms

If you’ve had the flu before, you know it’s not fun. The influenza virus typically comes with well-known symptoms, including:

  • Fever
  • Cough
  • Fatigue
  • Sore throat
  • Body aches
  • Headaches

The flu tends to be seasonal, peaking in its prevalence in the autumn and winter months in countries in the northern hemisphere. The reason for the seasonal prevalence of the flu is not fully known, but some theories exist.

Some believe that the flu tends to rise in prevalence in the fall and winter months because the cold weather negatively affects the immune system, making people more susceptible to infection.

Others suggest that in winter, people spend more time inside and are then more likely to spend more time in close proximity to other infected people.

Some research also suggests that drier air makes transmission of the virus more likely because drier air allows the virus to carry more easily and because moisture warps the surface of the virus itself, making it more difficult for it to attach to a host.

Flu symptoms worsen over time after the initial infection. If you are healthy, your immune system should be able to fight it off within a few days.

STI symptoms

Sexually transmitted infections can be a bit tricky to diagnose since most of them are either symptomless or produce symptoms that can be attributed to other illnesses.


When the body has an infection, the immune system increases the body’s temperature in order to help fight the infection. This can happen in response to all sorts of infections, including viral, bacterial, and parasitic infections.

Since many STIs are caused by viruses or bacteria transmitted through sexual activity, the body naturally responds with a fever upon infection. STIs that can cause a fever include:


If a flu infection is bad enough, it can induce nausea or vomiting in the infected person. Viral and bacterial STIs that can cause vomiting include HIV, Syphilis, Hepatitis B.

General body aches/headaches

When the body gets an infection, it’s common to get generalised muscle or body aches and headaches. Many STIs can cause body aches, including:

  • Syphilis
  • HIV
  • Herpes
  • Hepatitis B

Sore throat

A common symptom of the flu, a sore throat is a less common symptom of an STI. However, there are certain circumstances where a sore throat can, indeed, be a sign of an STI.

Some STIs are site-specific and tend to remain at the original site of infection. STIs like Chlamydia and Gonorrhoea, for instance, tend to infect the genitals, as it is the main site where these infections are transmitted.

But it’s possible for these STIs to infect other parts of your body.

Since Chlamydia and Gonorrhoea only require a mucous membrane to be transmitted, it’s possible to get an infection in your throat. This can happen during oral sex or, in rare cases, through deep kissing.

Final thoughts

Flu symptoms and STI symptoms can be tricky to navigate, but now that you are aware of the differences, we encourage you to get tested with Better2Know if you think you may have been exposed to an STI.

Act now to secure your health and the health of those you care about. Call the number above to speak to one of our Sexual Health Advisors.

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