Chlamydia
A white or cloudy discharge and / or irritation, or stinging when urinating may develop two to four weeks after you're infected. Sometimes there are no symptoms.

In women it can cause pelvic inflammatory disease (PID). This may be painful, but just as often there are no symptoms. Symptoms of PID are vaginal discharge, pain and tenderness in the lower abdomen, fever, pain during sex, bleeding or spotting between periods.

In men it causes NSU (non-specific urethritis) which is also called NGU. This refers to any inflammation of the urethra (urine passage) that isn't gonorrhoea. It can be successfully treated with antibiotics but remember all partners must be treated.

Vaginitis
Some people get this when they take antibiotics or the contraceptive pill. The commonest form of vaginitis is thrush, also called monilia or candida. It produces an itchy, whitish discharge.

Gonorrhoea
Often called the jack, the drip or the clap. Symptoms usually occur within 3-7 days of sexual contact. In men this usually causes a discharge from the penis and pain (commonly described as 'pissing razor blades') but in women there may be no symptoms.

Like chlamydia, gonorrhoea can cause PID in women. Gonorrhoea commonly exists side-by-side with other STDs. It is treated with antibiotics.

Hepatitis A
A highly infectious virus which is spread by contact with saliva and faeces. For this reason, if you have anal sex or use your mouth on your partner's anus it is important to wash your hands after taking off the condom or rubber dam.

Hepatitis B
This virus is transmitted by sharing needles and syringes and through sex. It is highly infectious. Persistent infection can cause serious health problems.

Symptoms are jaundice which causes yellow skin, dark urine, fever, pale bowel motions, nausea and abdominal pain. A vaccine is available.

Syphilis
A bacterial infection which causes a painless ulcer to develop 10-90 days after exposure. You may not be able to see the ulcer if it is in the anus or vagina. The ulcer will heal but the disease remains.

In the second stage there may be headaches, sore throat, fever and a rash on the palms of the hands or the soles of the feet. The second stage symptoms, if they develop, usually occur 3-12 weeks after infection.

The third stage appears 2-20 years later. This includes severe heart and blood vessel or nervous system problems.

Syphilis can be treated successfully with antibiotics, the earlier the better.

Pubic Lice
Also called crabs, these infect the pubic hair and cause intense itching. They jump easily from one person to another.

They can be treated with preparations available from the chemist.

Clothing and bedding of infected people need to be washed in hot water and dried in the sun.

Genital Warts
These look like other warts but appear alone or in clusters on the skin around the penis, vagina or anus. They are caused by a virus (human papilloma virus) and are very easily spread during sex.

They are easy to see if they appear on the outside but are difficult to see if they are inside a woman's vagina or on her cervix.

Herpes
There are two types of Herpes virus: one causes oral ulcers and the other usually causes genital ulcers.

Painful, itchy blistery sores usually occur around the mouth, genitals or anus. It may be infectious at any time, but is more infectious when the sores are present.

There is no cure and it is possible for it to re-occur. However there are many treatments available to relieve any discomfort and to reduce the likelihood of recurrent episodes.

HIV and AIDS
HIV is a viral infection transmitted by the transfer of infected body fluids such as blood (including periods), semen, vaginal fluids and pre-cum either through sex or needle use.

People remain infected for life as there is currently no cure, so practising safe sex and safe needle use is essential to prevent the spread of the virus. You can't tell when someone has HIV unless a blood test for HIV antibodies is done. People who are HIV positive can remain well for years.

HIV infection is a slowly progressive illness which can eventually cause permanent damage to the immune system. This leaves the body vulnerable to certain rare infections. These infections indicate Category 4 of HIV which is also called AIDS and is the end stage of the illness. This can also last for some years and a person with AIDS can go in and out of being well.

Safe sex and safe needle use will prevent contact with HIV so being HIV positive or having AIDS doesn't mean no sex.