What are sexually transmitted diseases?Anyone having sex can get a sexually transmitted disease (S.T.D.) from an infected partner, if they do not use any protection (e.g. condoms).There are at least 25 different S.T.D.ís which are all spread during sex, this can mean through vaginal intercourse, oral sex or anal sex.If left untreated, S.T.D.ís can cause infertility and permanent damage to your health, therefore early diagnosis and treatment is very important. If you are worried about having an S.T.D. or are thinking of having a baby, it would be wise to visit your doctor or local G.U.M. clinic. Everybody can catch an S.T.D. even if you have been with your partner for some time, this is not necessarily because your partner has been unfaithful but because some infections can lie dormant in the body and may not cause symptoms.