A once-a-week application of the female hormone estrogen to the penis may act as a “natural condom” that helps protect men against HIV infection, suggest Australian researchers.

They said an estrogen cream could quadruple the thin layer of the protein keratin on the skin, providing a natural defensive layer, Agence France-Presse reported.

“You create what you could call a natural condom. You create a biological membrane which (HIV) can’t get through,” Professor Roger Short, of the University of Melbourne, said in an interview with the Australian Broadcasting System.

He said this method wouldn’t protect against other types of sexually transmitted diseases and wouldn’t prevent pregnancy, but could offer a safe and simple method of reducing HIV infection around the world, AFP reported.

Clinical trials are expected to be conducted in Africa. The research was outlined in the journal PLoS One.