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What are sexually transmitted diseases (STDs)?

Sexually transmitted diseases (STDs) are diseases that are mainly passed from one person to another during sex. There are at least 25 different sexually transmitted diseases with a range of different symptoms. These diseases may be spread through vaginal, anal and oral sex.

Most sexually transmitted diseases will only affect you if you have sexual contact with someone who has an STD. However there are some infections, for example scabies, which are referred to as STDs because they are most commonly transmitted sexually, but which can also be passed on in other ways.

  What are sexually transmitted infections (STIs)?

Sexually transmitted infection (STI) is another name for sexually transmitted disease (STD). The name STI is often preferred because there are a few STDs, such as chlamydia, that can infect a person without causing any actual disease (i.e. unpleasant symptoms). Someone without symptoms may not think of themselves as having a disease, but they may still have an infection that needs treating.

  How can you tell if you have a sexually transmitted disease?

You may become aware that you have an STD because of symptoms, or it may be that a sexual partner tells you they have an STD which they might have passed on to you. Some sexually transmitted diseases can be transmitted by an infected person even if they don't have any symptoms. Certain STDs can also be transmitted from a pregnant woman to her unborn child.

If you think you might have been exposed to an STD then you should go to see a doctor. Many sexually transmitted diseases can be easily cured, but if left untreated, they may cause unpleasant symptoms and could lead to long-term damage such as infertility. It is important that anyone diagnosed with an STD informs everyone they have had sex with within the past year (or everyone following the partner they believe may have infected them).

What are common STD symptoms?

STD symptoms vary, but the most common are soreness, unusual lumps or sores, itching, pain when urinating, and/or an unusual discharge from the genitals.

To see pictures of common STDs, please visit our STD pictures page.

Which are the most common sexually transmitted diseases?

Below are some of the most common STDs and other genital diseases. To find out more about HIV, visit our HIV page.

Bacterial Vaginosis

Bacterial Vaginosis (BV) is caused by an imbalance in the normal healthy bacteria found in the vagina. Although it is relatively harmless and may pass unnoticed, it can sometimes produce an abundance of unpleasant fishy smelling discharge.

BV is not strictly an STD as it is not transmitted via sexual intercourse. However, it can be exacerbated by sex and is more frequently found in sexually active women than those who have never had intercourse.

Whilst there is no clear explanation as to why BV occurs, there have been suggestions that the alkaline nature of semen could be one cause, as it may upset the acidic nature of the vaginal bacteria. Another cause can be the use of an intrauterine contraceptive device (coil).

A woman cannot pass BV to a man, but it is important she receives treatment as BV can occasionally travel up into the uterus and fallopian tubes and cause a more serious infection. Treatment for BV consists of applying a cream to the vagina or taking antibiotics.

Chlamydia

Chlamydia is one of the most commonly reported bacterial sexually transmitted diseases. It is caused by the chlamydia trachomatis bacterium. It infects the urethra, rectum and eyes in both sexes, and the cervix in women. If left untreated, long-term infection can lead to fertility problems in women. Chlamydia is transmitted through genital contact and/or sexual intercourse with someone already infected. Symptoms of chlamydia usually show between 1 and 3 weeks after exposure but may not emerge until much later.

Crabs or Pubic Lice

Enlargement of Phthirus pubis, the pubic or crab louse Enlargement of Phthirus pubis, the pubic or crab louse.

Crabs or pubic lice are small crab-shaped parasites that burrow into the skin to feed on blood. They live on coarse body hair, predominantly pubic hair, but can also be found in armpit hair, facial hair and even on eyelashes. The lice are yellow-grey in colour and use their crab-like claws to grip hair strands. They can sometimes be spotted moving on the skin.

Crabs are easily passed on during sex, but can also be passed on through sharing clothes, towels or bedding with someone who has them. Crabs cannot be transmitted via toilet seats or swimming pools.

Symptoms of crabs are usually noticed around 5 days to 7 weeks after infection and include:

  • itchy skin;
  • inflammation of the affected area;
  • sometimes visible lice and eggs;
  • spots of blood as lice feed from blood vessels in the skin.

Although there is no effective way to prevent becoming infected during sex, a person who has crabs can reduce the risk to others by washing bedding, towels and clothes on a hot wash to kill off the parasites.

Treatment for public lice is easy, consisting of special shampoos, lotions and creams that kill the lice and their eggs. It is not necessary to shave pubic hair as this is unlikely to remove all lice.

Genital warts

Genital warts are caused by some sub-types of human papilloma virus (HPV). They can appear on the skin anywhere in the genital area as small whitish or flesh-coloured bumps, or larger, fleshy, cauliflower-like lumps. They are unlikely to cause pain but may itch and can be difficult to spot. Often there are no other symptoms of genital warts, but if a woman has a wart on her cervix she may experience slight bleeding or unusual coloured vaginal discharge.

Gonorrhea

Gonorrhea (once known as the clap) is a sexually transmitted infection that can infect the urethra, cervix, rectum, anus and throat. Symptoms of gonorrhea usually appear between 1 and 14 days after exposure, but it is possible to have no symptoms. Men are more likely to notice symptoms than women. Symptoms can include:

  • a burning sensation when urinating;
  • a white/yellow discharge from the penis;
  • a change in vaginal discharge;
  • irritation or discharge from the anus (if the rectum is infected).

Hepatitis

Hepatitis refers to viral infections that cause inflammation of the liver. Several different types of hepatitis virus exist (labelled A to G), with hepatitis A, B and C being the most common. Hepatitis can occur following excessive and prolonged consumption of alcohol or the use of certain medicines and drugs, but it is most commonly caused by a virus. Read more about the different transmission routes of hepatitis.

Herpes

Herpes is caused by two strains of the herpes simplex virus, type 1 (HSV-1) and type 2 (HSV-2). HSV-2 is more common and usually manifests itself in the genital and anal area, whereas HSV-1 is more likely to affect the mouth and lips in the form of cold sores. On a global scale, HSV-2 is a very common STD. Symptoms of herpes usually appear 2 to 7 days after first exposure to the virus and last 2 to 4 weeks. Both men and women may have multiple symptoms, including:

  • itching or tingling sensations in the genital or anal area;
  • small fluid-filled blisters that burst leaving small painful sores;
  • pain when passing urine over the open sores (especially in women);
  • headaches;
  • backache;
  • flu-like symptoms, including swollen glands or fever.

Once the first outbreak of blisters has gone, the herpes virus hides away in nerve fibres near the infection site, where it remains dormant, causing no symptoms. Symptoms may come back later (particularly during times of stress and illness) but usually in less severe and shorter episodes. Read more about herpes.

Molluscum contagiosum

Molluscum contagiosum (MC, also known as water warts) is a common viral infection, which results in a skin disease. Small papules usually appear on exposed skin such as the torso, thighs, genitalia and anus, around 2 to 8 weeks after initial infection with the virus. The pearl-shaped papules are usually between 1 to 5 millimetres in diameter, are filled with a gungy, white, contagious, fluid, and often appear in clusters.

MC can be transmitted through direct skin-to-skin contact and also indirectly through sharing towels, baths or clothing with someone infected. It is not strictly an STD as it often occurs in children, especially those prone to skin conditions such as eczema. Children are more likely to assist transmission by scratching the infected sites, although it should be noted that the chance of passing on the virus is small.

MC is grouped with STDs because of the risk of transmission through close body contact during sex, which is why it is often screened for in sexual health clinics. The risk of becoming infected with MC can be reduced by:

  • Using condoms during sex, although this only offers partial protection as MC can be passed on by anal/genital lesions not covered by the condom.
  • Covering affected areas of skin (where possible) with clothing or sterile dressings.
  • Not sharing baths, clothing and towels.
Molluscum lesions on an arm Molluscum lesions on an arm.

The recommended treatment is often to leave MC to clear up by itself (which usually takes around 6 to 18 months) as medical removal can leave scarring. If requested, the lesions can however be removed by various medical treatments such as cryotherapy (freezing), diathermy (burning), or currettage (cutting or scraping).

In an HIV-positive person, a large outbreak of molluscum contagiosum may indicate that the immune system is critically weak and it is advisable to seek medical attention.

Scabies

Scabies is an intensely itchy, contagious skin infestation of the parasitic mite Sarcoptes scabiei. The adult female mite is around 0.4 mm (one sixtieth of an inch) long and barely visible to the human eye, with the male being half that size. Female mites burrow into the outer layer of the skin (stratum croneum) to lay eggs. Symptoms begin 2 to 6 weeks after infection and include:

  • Burrows that appear as silvery or brown wavy lines up to 15 millimetres (half an inch) in length. The burrows can appear anywhere, but usually occur on the webbing between fingers and toes, on the genitals, around the anus, or on the buttocks, elbows or wrists.
  • An intensely itchy rash of inflamed pimple-like lumps (papules/lesions) as an allergic reaction to the mites, their eggs and faeces.
  • Widespread itching, particularly at night or after baths when the body is warmer, as a reaction to the mites.

Again, scabies it not strictly a sexually transmitted disease, as the scabies mite can be passed on through other forms of prolonged direct skin contact. Scabies has been known to spread rapidly in crowded conditions where there is frequent contact between people, such as in care homes or child care facilities. It is also possible, but much less likely, to acquire the infestation through sharing clothes, towels or bedding with someone infected. Sexual activity does however carry a particularly high risk of transmission.

There is no effective way to prevent infection apart from avoiding direct skin contact with an infected person. If a person knows they are infected then they can prevent the infestation spreading by washing clothes and bedding on a hot wash to kill the mites (at 50 degrees Celsius / 120 Fahrenheit or above). Treatment comes in the form of lotions that can be bought from pharmacies without prescription and applied to the body to kill the parasites. It is recommended that all people in close contact, such as sexual partners or members of the household, should be treated at the same time, even if they are not yet showing any symptoms of infestation.

Syphilis

Syphilis is a bacterial infection caused by Treponema pallidium, which used to be known as the pox. It is usually sexually transmitted, but can also be passed from an infected woman to her unborn child. Syphilis progresses through several stages, of which the primary and secondary stages are very infectious. Syphilis symptoms can be difficult to recognise and may take 3 months to appear after sexual contact with an infected person. They include:

  • one or more painless ulcers on the penis, vagina, vulva, cervix, anus or mouth;
  • small lumps in the groin due to swollen glands;
  • a non-itchy rash;
  • fever or flu-like symptoms.

Left untreated the infection progresses to a latent stage. This may be followed by tertiary syphilis, which can seriously affect organs such as the heart, and can sometimes lead to death.

Thrush

Thrush, also known as candidiasis, is a yeast infection caused by the Candida species of fungus. Thrush is not technically a sexually transmitted infection, as Candida is a common yeast that is found on the skin and genitals of most people, even those who have not had sex. Candida is usually suppressed by the immune system and the natural bacteria found in the body, but there are many things that can upset the balance and allow Candida to grow. Thrush occurs a lot less frequently in men.

The symptoms of a thrush infection are:

  • In women - irritation, itching, thick white discharge, redness, soreness and swelling of the vagina and vulva.
  • In men - irritation, discharge from the penis, difficulty pulling back the foreskin usually caused by the swelling of the head of the penis (balanitis).

There are many causes of thrush, but the most common are:

  • In women, wearing nylon or lycra clothes that are too tight (the lack of air circulation can cause Candida to proliferate).
  • Certain antibiotics or contraceptive pills that alter the pH balance of the vagina.
  • A change in the hormonal balance in pregnant women, causing a change in the level of normal bacteria.
  • Spermicides (found on some condoms) or perfumed toiletries that irritate the vagina or penis.
  • Douching (washing out the vagina) or using tampons.
  • Sexual contact (either genital or oral) with someone who carries the candida yeast.

Treatment for thrush involves applying an anti-fungal cream that contains clotrimazole. If an infection is recurring then fluconazole may be prescribed to be taken orally, unless the patient is pregnant. It may also be suggested to wash the genitals with water to avoid irritation and to wear loose fitting cotton underwear and clothes.

Trichomoniasis

Trichomoniasis (also known as Trich) is caused by the single-celled organism trichomonas vaginalis, which is transmitted through sex. It can infect the vagina and the male and female urethra. Often this STD presents no symptoms, though women are more likely to have symptoms than men. If symptoms do appear, they can include:

  • discharge in both men and women (sometimes copious and unpleasant smelling in women);
  • discomfort or pain whilst having sex;
  • pain when urinating and inflammation of the urethra.

Women may also experience an inflammation of the vulva and they may develop cystitis (an infection of the urinary system).

Transmission is usually through vaginal, anal or oral sex with an infected person. The most effective prevention method is to practise safer sex by using condoms.

Treatment for both men and women is a drug called metronidazole which can be taken orally or applied as a gel. It is important for any sexual partners to also be treated as trichomoniasis can be carried and spread without symptoms. If a woman is pregnant then she should seek medical advice before pursuing treatment.