Wearing a condom stops the genital secretions of the other person from coming into contact with the mucous membranes of your genital tract during sex. If it is worn the whole time, it can prevent the transmission of AIDS. AIDS can be transmitted through sexual intercourse mainly because the other person’s genital secretions come into contact with the mucous membranes of one’s own body. Or if one’s mucous membranes are torn, it is easier to spread AIDS. As long as condoms are worn throughout, this exchange of fluids can be prevented, thus stalling the transmission of AIDS. So when a condom is worn for sex, if it is not worn the whole time or if the condom is torn and fluid exchange occurs, you take that risk. Of course, this is for the case where one of the partners is HIV positive and the other is normal.