Australian scientists are working on a new gel-based contraceptive that will protect against sexually transmitted infections (STIs) as well as preventing pregnancy.

It's still at least a decade off, but Professor John Aitken, says the gel could be applied to a small, pliable sponge and inserted in the vagina up to 48 hours before sexual intercourse.

As soon as semen makes contact with the gel, the sperm are paralysed and any STI-causing organisms are killed.

At present, there are not any ''local compounds'' available that can be applied to prevent STIs, just the ''classic'' spermicide, which was a ''crude inhibitor of fertility'', Professor Aitken said.

''Women who use a lot of this stuff, especially commercial sex workers, are significantly more likely to get HIV than women who don't use it ... it just destroys everything around it,'' he said.

''Most of the time you want both right. You want to be able to have intercourse in the safe knowledge you will neither get pregnant, nor will you catch some terrible microbe.''

Professor Aitken, a reproductive scientist at the University of Newcastle in NSW, said the product being developed would be aimed at women between the ages of 15 and 25.

''(These people) are the ones who are more susceptible to sexually transmitted disease and unwanted pregnancies,'' he said.

Professor Aitken said there have been no new forms of contraception since the pill was introduced in 1959.

''We're now in a completely different environment,'' he said.

''We need contraceptives that meet the demands of the 21st century and one of those demands is that there's now a much higher risk of contracting a sexually transmitted disease than there was in the 1950s and '60s.

''HIV didn't exist then - or at least it was very confined - and chlamydia has become a huge problem.

''Globally there is a pandemic in sexually transmitted disease so we need to develop new forms of contraception that take that into account.''

Chlamydia is the most common infectious disease of any kind, Professor Aitken said.

If left untreated, it can affect men's and women's reproductive health and lead to infertility in both sexes.

However, testing for chlamydia involves a simple urine test and it can be treated by a single dose of antibiotics.

Meanwhile, 46 million abortions are performed each year because of contraceptive failure, Prof Aitken said.

"If we can stop young people getting pregnant unintentionally and we can protect them against sexually transmitted disease then that is a win-win.''

The agents have been developed and the chemistry is being tested, said Prof Aitken, who spoke at the Shine Dome in Canberra this week.

Animal and human trials will follow before the contraceptive can be released to the public.

- AAP