Scabies is a skin infestation due to a tiny, parasitic mite, Sarcoptes scabiei. The males live on the surface of the body, but females burrow into the skin to feed and lay their eggs, which take around two weeks to hatch. As well as being sexually transmitted, scabies can be passed on in a number of ways, including shaking hands, sharing clothes, gloves or bed linen.

What symptoms will you notice?
The burrowing produces characteristic eruptions with fine, crooked, raised lines around one to two centimetres long. The tracks soon become scaly and inflamed due to an allergic reaction to the mites' faeces, which are also deposited under the skin.

Intense itching develops, resulting in self-inflicted scratch marks, weeping sores and scabs - hence the common name.

Scabies mites are attracted to skin folds, which are warm and protective. If caught during intimate sexual contact, they may first appear around the genitals. They may also infect the finger webs, armpits and inside the elbows, although they can occur anywhere on the body except - usually - the face.

How is scabies diagnosed?
The mites are sometimes looked for under a microscope, but diagnosis is usually obvious on examination.

How is scabies treated?
Anti-scabies lotions (scabicides): These can be bought over the counter to kill adult mites. Different treatments may be recommended at different times depending on local patterns of resistance. Some lotions also kill the eggs, but others need to be reapplied to kill newly hatched mites.

Apply lotions at night to cover all skin from the neck down, sparing the head and face. Pay particular attention to the webs of fingers and toes, and brush lotion under the ends of nails. Don't wash hands after applying lotion or it will need to be reapplied. Usually, only one application is needed. Wash off by bathing again 12 - 24 hours later. Taking an oral antihistamine that will aid sleep and/or crotamiton cream, which has a mild scabicide action and anti-itch properties, can reduce itching.

If infection proves difficult to eradicate, it may help to use clean bed linen every night and fresh clothes each morning during treatment so you don't re-infect yourself from these sources, although these measures are no longer thought to be routinely necessary.

Itching and scaliness can last for two or three weeks after treatment due to the continued presence of mites' faeces in the skin. Using tea-tree products on your skin (for example, soaps, lotions) may help to reduce the risk of re-infection.

As scabies is so infectious, all sexual contacts and members of the affected person's household should be treated at the same time.

If you're worried you have an STI or want to find out more, check out the symptoms, diagnosis and treatments for:

• Chlamydia
• Genital herpes (HSV)
• Genital warts
• Gonorrhoea
• HIV and AIDS
• Pubic lice
• Syphilis
• Trichomonas