The Centres for Disease Control and Prevention (CDC) has issued a warning to sexually-active Americans to stop washing and reusing condoms – because, unbelievably, “people do it.”

In a tweet linking to condom and STD facts and statistics, the health agency wrote: “We say it because people do it: Don’t wash or reuse condoms.

“Use a fresh one for each sex act,” the CDC advised.

In response to the Twitter warning, people were amused that it is not obvious condoms should not be washed after use.

When used properly, condoms are highly effective in preventing pregnancy and sexually-transmitted STDs, including human immunodeficiency virus (HIV).

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However, considering fewer than half of US high schools met the CDC’s requirement for sexual education in 2015, the need for the warning is not surprising.

According to a health report published by the CDC in 2017, only one-third of Americans use condoms – and many may be doing so incorrectly.

In a 2012 study published in the journal Sexual Health, co-author and University of Kentucky professor Richard Crosby said researchers “chronically underestimated how complicated condom use can be,” after finding 1.4 to 3.3 per cent of respondents had reused a condom at least twice during a sexual encounter.

Reusing male condoms results in weakened latex, which can lead to rips or tears that increase the risk of pregnancy and STDs.

As the number of STD and STI cases in America continues to rise, with more than two million cases of chlamydia, gonorrhoea and syphilis reported in 2016, according to the CDC, correct condom-use is more important than ever.

For condom-use to be effective, the CDC states that a new condom should be used “for every act of vaginal, anal and oral sex throughout the entire sex act (from start to finish).”