The more common STDs are well known, but sometimes an STD test will produce a truly unusual result. Like one of these five rare STDs...

Anyone with a passing knowledge of STDs will be aware of some of the more common infections – gonorrhoea, chlamydia, genital herpes, and so on. If you go for an STD test, these are amongst the most likely diseases that could be found, but they are by no means the only ones – there are many rare infections that may not occur as often, but can be just as dangerous. Some of them were once common, but have been driven back by improvements in medical knowledge, whereas others used to be rare, but are becoming increasingly common for one reason or another.

Here are five rare STDs that most people know little about...

Chancroid

This STD is still common in Third World countries, but is relatively rare in the developed world. Manifesting as a series of sores on the genitals, Chancroid is painful but not serious, and can be cured with a simple course of antibiotics. An STD test is not usually necessary, as a doctor will be able to recognize the distinct sight of the sores.

Syphilis

Syphilis used to be one of the most common STDs. In his entry for it in his 'Dictionary of Received Ideas', 19th century French author Flaubert listed the disease as "Syphilis: Pretty much everyone has it." It also used to be one of the most feared. It was known as 'The Great Imitator' due to how difficult it was to diagnose, with no accurate STD test for it. There was no effective treatment until the 20th century.

Thanks to advances in medicine, especially antibiotics, syphilis is now thankfully very rare. This is something to be grateful for, especially given that the later stages of syphilis, once it had spread to the brain, usually resulted in madness, disfigurement and death!

Molluscum contagiosum

The name sounds intimidating, but if this crops up on an STD test, it's nothing to worry about! Manifesting as a series of bumps, rashes and lesions, molluscum contagiosum is spread by sexual or skin to skin contact. It's a trifle unsightly but fairly harmless, and most doctors will let it go away on its own, which usually takes 3 to 6 months.

Lymphogranuloma venereum

Lymphogranuloma venereum (generally shortened to LGV) was rare until recent years, but it is now becoming more common in developed nations. A variant of the chlamydia virus, it causes swelling and enlargement of various glands in the body, sometimes to a dangerous degree. This STD is highly variable in effect – it is usually just painful and uncomfortable, but in rare cases it can be fatal. The disease can usually be easily treated if it is caught early.

Granuloma inguinale

Sometimes mistaken for syphilis or chancroid, granuloma inguinale causes small painless ulcers and warts on the affected areas. These burst, spread and continue to grow as the disease progresses, making it a dangerous infection if it is left untreated. However, just like many of these rare STDs it can be treated with antibiotics, so there is a very low risk of infection in developed countries.