The World Health Organization's guidance applies to all travelers, whether or not they show symptoms of the virus.
The organization's previous guidance in early June was for only men without symptoms to use condoms or abstain from sex for eight weeks after returning from areas with epidemics.
The disease is mostly transmitted by mosquitoes but can also be spread via sex.
Officials had previously tracked cases of men spreading Zika through sex and in July, American scientists reported the first case of a woman infecting a male partner via sex.
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Most people who catch Zika only experience mild symptoms like fever and a rash, but in a small proportion of pregnant women, the virus can also cause brain and other neurological problems in babies.
WHO says men and women living in areas with ongoing Zika epidemics should make an "informed choice about whether and when to become pregnant."
Since the virus arrived in Singapore about two weeks ago, it has sickened nearly 300 people.
WHO said it was still unsure what percentage of Zika-infected women will give birth to a brain-damaged infant, calling the risk "relatively low but significant.
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