In the UK there are several common STIs, some of which are well known and others, less so. Here's a round up of their symptoms and treatments.

1. Chlamydia is a bacterial infection and one of the most common STIs, though many people don’t have any symptoms and so don’t know they have it, which means they may unwittingly pass it onto others. Symptoms, if they occur, can include pain when urinating; unusual discharge from the vagina, penis or back passage; testicular pain and swelling; and bleeding between periods or after sex. The main problems really develop if it is left untreated and spreads to other parts of the body, as it can cause issues such as pelvic inflammatory disease, inflammation of the testicles, and infertility. A single antibiotic dose is the usual treatment.

2. Gonorrhoea is a bacterial infection sometimes known as “the clap”. Symptoms can include pain when urinating, a yellow or green discharge from the vagina or penis, and bleeding in between periods. Around 10 per cent of men and nearly half of women with the infection have no symptoms at all. If not treated, it can spread to other parts of the body and cause problems such as pelvic inflammatory disease, which can cause pelvic pain, infertility and ectopic pregnancy. In pregnancy, gonorrhoea can cause miscarriage and premature labour. In men, gonorrhoea can result in the testicles and prostate gland becoming infected, which can reduce fertility. There is also a small chance of sepsis developing. The most common treatment is an antibiotic injection plus a single oral antibiotic.

3. Syphilis is another bacterial infection that can be symptomless. Those who do get symptoms may experience small, painless sores or ulcers most commonly in the ano-genital region but sometimes in other places such as the mouth; a blotchy red rash on the palms of the hands or soles of the feet; small wart-like growths on the vulva or anus; and white patches in the mouth. Non-specific symptoms may also occur, such as tiredness, achiness, fever and swollen glands. If left untreated, syphilis can spread to other parts of the body, including the brain, and cause serious problems. Syphilis is usually treated with a single antibiotic injection, though more may be needed if the infection has been present for a long time. Oral tablets are an alternative.

4. Trichomoniasis is a parasitic infection. Up to half of all people who have it won’t develop any symptoms, but women may notice a yellow-green, smelly discharge from their vagina; soreness, inflammation and itching around their genital area; and discomfort when urinating or having sex. Men may experience pain during urination or ejaculation; discharge from the penis; and soreness, swelling and redness around the head of the penis and foreskin. They may feel they need to urinate more often than usual. Complications are rare, but women who contract it while pregnant may go into premature labour and/or have a baby with a low birthweight. A course of oral antibiotics is the usual treatment.

5. Genital herpes is a viral infection that can cause small blisters – usually within a week of contracting the infection, but they can take months or even years to appear – on and around the genitals. These burst to leave red, open sores and symptoms also include a feeling of tingling or burning around the genitals, pain upon urination and vaginal discharge. The condition cannot be cured, as once someone has the virus, it stays in the body, and though the symptoms usually clear up, they may recur. Antiviral tablets or cream can help if someone has very severe symptoms the first time they experience them.

6. Genital warts are caused by the human papillomavirus and the number of cases in the UK has dropped dramatically since the introduction of the HPV vaccine. The small, painless warts appear around the vagina, penis or anus, causing itching and sometimes changing the usual flow of urine. They can be treated – using topical treatments, or having the warts frozen or cut off – but not cured, though sometimes the virus does clear naturally over time.

7. Mycoplasma genitalium (MG) is a bacterial infection that is sometimes asymptomatic but can cause vaginal discharge, pelvic pain and bleeding after intercourse and between periods in women, and uncomfortable urination, discharge from the urethra and penile pain and irritation in men. It has been linked to pelvic inflammatory disease, infertility, premature birth, miscarriage and stillbirth. Two different antibiotics usually need to be taken to treat MG.

8. HIV is a virus that damages the immune system, making it more difficult for infections and diseases to be battled. When the human immunodeficiency virus (HIV) has caused irreversible harm to the immune system, the condition is classed as acquired immune deficiency syndrome (AIDS). This is characterised by the onslaught of potentially life-threatening illnesses, such as recurrent pneumonia. There is no cure for HIV, but it can be managed so effectively that sufferers don’t go on to develop AIDS or its associated problems and live more or less as normal.