Dr Sermed Mezher (@drsermedmezherexplains) has made a name for himself online by sharing some little-known health warnings. From why you shouldn't make your bed first thing in the morning to the common causes of chest pain and signs of ADHD, there are no corners left uncovered.
But one video, in particular, has racked up more than a million views uncovers one thing to look out for when using a public bathroom.
In the original clip, Dr Mezher showed an image of a toilet paper roll with small red markings.
"If you go to a public restroom and the toilet paper looks like this, do not use it," he urged viewers in the since-deleted TikTok clip. "That's because these marks are signs that intravenous (IV) drug users are trying to clean their needles to be able to rthemse it again."
It didn't take long for hundreds of fellow TikTokers to take to the comments, with one writing: "I could have gone my whole life without knowing this."
Another added: "Reason 10278651 why I can’t use public toilets."
Many more took the insight as a sign to carry pocket tissues in future.
In an updated clip, Dr Mezher highlighted that there have been "zero cases of HIV or hepatitis transmission in this way," referring to the dry blood-stained tissue paper.
In the caption, he explained: "HIV and Hepatitis viruses cannot be transmitted through toilet paper because these viruses require specific conditions to survive and transmit from person to person."
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