STIs can be easy to miss, due to their capacity to be symptomless.

Just because you don’t see any visible signs, doesn’t mean you don’t have one. It’s important to keep in mind that, even when an STI doesn’t produce any physical effects, it can still be passed on from one person to another through a variety of sexual channels.

Granted, it’s absolutely more likely for someone who has multiple sexual partners to contract an STI than someone who doesn’t. But while some people may be more susceptible to them than others, no-one is immune to their effects.

So how do you know whether or not you have an STI?

Here we will discuss their common signs and symptoms, and highlight how these may differ between men and women.

Chlamydia

The most common STI in the UK, with over 200,000 new cases diagnosed each year, this infection is caused by a bacteria called chlamydia trachomatis, and can be transmitted via unprotected anal, vaginal or oral sex, or the sharing of sex toys.

How do I know if I have it?

Both men and women may present urinary pain, and genital discharge. This may mean a change in consistency in vaginal discharge; or a thin, white and cloudy discharge emanating from the penis.

Women may also notice pain in the lower abdomen, bleeding between periods, and heavier bleeding during menstruation.

In addition, men may notice testicular pain.

Sometimes, chlamydia can affect the eyes, and cause conjunctivitis symptoms such as redness, ocular discharge and pain.

What is important to note, however, is that chlamydia often does not cause any symptoms. 80 per cent of female cases and 50 per cent of male cases are completely asymptomatic.

Left untreated, the condition can lead to infertility, and other complications.

Gonorrhoea

Gonorrhoea is a bacterial illness easily transferred from one person to another by any form of unprotected sex.

Gonorrhoea can be present in both males and females without any obvious symptoms showing.

The number of men being diagnosed with Gonorrhoea has recently spiked, with over 20,000 diagnoses being made in 2013, a dramatic increase when compared to around 10,000 cases in 2008.

How do I know if I have it?

Both men and women should look out for an unpleasant green or yellow discharge emanating from either the penis or vagina.

As with chlamydia, gonorrhoea can transfer to the eyes, rectum and throat causing swelling, discharge and discomfort in both males and females.

Women can develop: a painful burning sensation when urinating; a tender feeling in the lower abdomen; bleeding between periods; or heavier periods.

Men should look out for: swollen foreskin; pain when passing urine: or tender tesitcles.

That being said, around 10 per cent of male cases and 50 per cent of female cases are asymptomatic and demonstrate no symptoms at all.

Without treatment gonorrhoea can again cause more serious health problems including infertility.

Syphilis

Treponema pallidum is the name of the strain of bacteria that causes syphilis.

The disease is much more common in males than females, with about 80 per cent of recorded cases being in men who have sex with other men.

How do I know if I have it?

The illness goes through three phases. For both men and women it is initially characterised in its primary stage by a small sore or ulcer, known clinically as a chancre.

The often-overlooked painless sore develops at the site of transmission which could be on the penis, vagina, anus, fingers, mouth, lips or buttocks. Lymph glands can also swell up.

Secondary syphilis symptoms develop a few weeks after the sore has healed.

This stage of the illness presents itself in both genders through a skin rash, most noticeably on the hands and/or feet, and small skin growths can be found on the anuses of both genders or the female vulva. The person may also experience weight loss, hair loss, a flu-like feeling or swollen lymph glands.

These symptoms may go through periods of flare up for several months until the latent phase is reached.

At this point no symptoms are actively displayed but the infection is still present. During stage one and two syphilis can be treated in a relatively uncomplicated manner using antibiotics.

If syphilis reaches its tertiary phase, then it is possible for serious and life-threatening complications to develop.

Herpes

Genital herpes is more common in women than in men.

It is an infection caused by the herpes simplex virus (HSV) and can result in painful blisters forming on the genital areas. It is easily transferred by skin-to-skin contact from any mucous membrane.

How do I know if I have it?

Spotting a herpes infection is not easy for either sex because signs of infection are not consistently present.

Genital herpes may be recognisable by painful blisters mostly focused on the genital area.

However, different strains of HSV can infect different mucous membrane areas. For example HSV-1 tends to infect the mouth whereas HSV-2 tends to infect the genitals. The common symptoms for both men and women are blisters on the genitals; pain when urinating and flu-like symptoms.

On top of this, women should also look out for vaginal discharge and blisters on the cervix.

Recurrent outbreaks of the condition tend to be less severe and last for a shorter period of time.

Once the virus is contracted it continues to live in the body indefinitely, although symptoms will not always be present. Treatment can be sought to help curb symptoms but there is no cure.

Genital Warts

Recent data ranked genital warts as the second most common STI in the UK

The warts are caused by human papillomavirus, more commonly known as HPV, and are transmitted by skin-to-skin contact.

How do I know if I have it?

Small growths form in and around the genitals, one single wart might appear or a cluster of several warts which can have the look of a ‘cauliflower’.

Both men and women can contract the condition but the warts might appear in different areas of the body.

For females the most common places for them to develop include inside the vagina, on the vulva, the cervix, upper thighs or anus.

Males might see warts develop on their penis, anus, urethra, scrotum or upper thighs.

Symptoms do not necessarily occur instantly and the virus can lay dormant for several weeks or months. The warts themselves are mostly painless but in some cases an itching or burning sensation is experienced.

Certain strains of the HPV virus can lead to cervical cancer in women.

TV

Trichomoniasis (TV) is an STI caused by a parasite called trichomonas vaginalis and is thought to affect around 6,000 people in the UK each year.

Up to half of those with the condition do not display any obvious symptoms. The parasite is transferred from person to person through unprotected sexual intercourse.

How do I know if I have it?

Females might experience any of the following symptoms: irregular vaginal discharge which looks thick, thin or frothy and may be a yellow-green colour; the discharge may have an unpleasant smell; pain and inflammation around the vagina; an itching feeling on the upper thighs; pain when passing urine or having sex and a tender lower abdomen.

Males should look out for an infected urethra, foreskin, or prostate gland. Trichomoniasis can also cause men to experience: pain during urination or ejaculation; a need to urinate more often; or a thin white discharge or soreness around the head of the penis known as balanitis.

The symptoms of TV are quite similar to other STIs and can cause some difficulty getting a diagnosis. Your GP or local GUM clinic can swab the infected area for testing and males may also be asked to provide a urine sample.

BV

Bacterial vaginosis (BV) is not categorised as an STI although it can cause symptoms which are similar to the conditions listed above.

The bacteria causes infected women to produce a thin, grey vaginal discharge which can have an unpleasant smell. Lots of women do not know that they have BV because they don’t develop noticeable symptoms.

BV is not a serious condition and can be easily treated with oral antibiotics.

So, how do I know if I have an STI?

As discussed above many STIs are asymptomatic, meaning that the bacteria, virus or parasite that causes the condition can be present in the body but not show any obvious symptoms. Therefore it is important to be regularly tested if you have unprotected sex.

If you are concerned that you might have an STI then you can get tested at a sexual health clinic, GUM (genitourinary medicine) clinic or at your GP. The majority of STI tests are simple and some can even be carried out in your own home.