Although men are sometimes culturally encouraged to have multiple sex partners, women also engage in various sexual activities that may influence their chances of contracting HIV/AIDS, be exposed to violence and unwanted pregnancies. While men and women are exposed differently to HIV/AIDS, they are both strongly influenced by it. Oftentimes, a woman's role and position in society will determine her chances of contracting HIV/AIDS. A look at age asymmetries in sexual relationships and condom use would better the understanding of power relations between genders. Age asymmetries are also important factors in in sexual relationships, in addition to gender-based power differences. Therefore girls' abilities to negotiate safe sexual behaviours are oftentimes limited. In South Africa, if a couple is estimated to be in a relationship and violence or sexual violence occurs, bystanders are unwilling to come to assist the woman in question. Oftentimes, if women sell sex publicly, it is acceptable to beat and rape her. Fish-for-Sex in Zambia also proves gender violence against women in need. Fishermen, for example, refuse to sell fish to a female trader if she does not accept to sexually engage with him.