A woman went viral when she discovered black mold in her reusable straw and thought it made her sick. A doctor explains why there's no need to panic.

• A TikToker said she found black mold in her reusable straw and thought it was making her unwell.
• Commenters began to weigh in with speculation and concerns about the impact of mold on her health.

A TikToker went viral and caused widespread concern when she discovered black mold in her reusable water bottle straw and became convinced it's the reason she's been unwell for the past three years.

"I feel so sick about this," said Kayla Houlihan, at the beginning of a video from April 3 that has since received 2.2 million views.

Posting from the account of her Australia-based brand Tribe Skincare, she began to recount a personal experience, explaining that she uses a reusable water bottle every day at work, and only fills it with water. One day, when she inspected its reusable straw, she found chunks of black mold, she said.

Not only was Houlihan disgusted by the mold, which she posed a photo of, but she also shared a theory with her viewers about the effects she thought it was having on her body. The TikToker said she has been sick for the past three years with stomach issues, and hasn't gotten a clear answer from medical professionals about why. She suggested the mold was the hidden cause of her problem.

Houlihan posted a series of clips explaining her theory further, and viewers began to weigh in with their thoughts on her viral revelation. The reaction revealed confusion about how to properly sanitize reusable water products, as well as the potential risks of not doing so.

Insider spoke to experts to get to the bottom of it, and while it's unlikely the mold caused Houlihan's symptoms, there is a valuable lesson in her story, they said.

TikTokers believe the moldy straw made Houlihan sick, but a doctor said that's unlikely

The day after posting her original video, Houlihan shared more details about her health, saying she has struggled with unpredictable nausea and vomiting, and had already undergone a number of tests to eliminate potential causes.

She said she noticed she felt sick mainly on weekdays, making her think her symptoms could have been caused by the water bottle, which she keeps on her desk at work.

Her videos drew a huge reaction. Some people questioned her theory and speculated about other health conditions that could have been causing her symptoms, but many viewers seemed convinced the straw was to blame, leading to panic from some about the impact of mold consumption. Some commenters said Houlihan's video made them concerned about mold in their own reusable bottles, which they decided to thoroughly clean out or throw out after seeing her video.

David Denning, a professor of infectious disease at the University of Manchester, UK, who has researched and written papers on fungal infections, told Insider that mold gives off mycotoxins, substances toxic to humans that can make them unwell, but it's unlikely that Houlihan's moldy straw was to blame for her symptoms.

He explained that the reason people can get sick from breathing in mold in large quantities, such as in buildings, is due to the high level of exposure. Such a level of mycotoxins can cause health problems like asthma.

While it's possible that there would be some mycotoxin in the straw, he doubts it's enough to make someone really sick.

The fact that Houlihan was drinking through the straw for two years implies "chronic exposure," Denning said, which could produce symptoms such as fatigue and coughing. But it's unlikely to cause the gastrointestinal symptoms she described, he said.

That's in part because our stomachs have lots of acid that kills some fungi — including mold — and it's only likely to make someone sick if there are lots of mycotoxins produced, he said. A 2018 study found that while mycotoxins can cause gastrointestinal issues, most people will be able to eliminate the mycotoxins naturally, provided they have good gut health.

Houlihan did not immediately respond to Insider's request for comment.

It's important to regularly wash reusable straws, even if they're only used for water

In her original TikTok, Houlihan acknowledged she was responsible for allowing mold to grow on the straw, noting that the brand she bought it from, sustainable-product retailer Frank Green, urges customers to wash their bottle with soapy water after every use on its website. The brand also sells small brushes for customers to clean their stainless steel straws.

Some commenters on TikTok said they were as surprised as Houlihan about the website's instructions, as they would not think to regularly wash a bottle they were only using for water.

But mold doesn't just grow on food. Mold spores can be airborne or carried on clothes and will begin to grow when they land in an area that is high in moisture.

According to a 2020 survey by research company CivicScience, 51% of people who don't make it a priority to use sustainable products overall still use a reusable water bottle — with 67% of environmentally conscious people doing the same. But it's unclear whether people are aware of how often they should clean these products.

To maintain good general hygiene, Sylvia Anderson, a food safety consultant based in London, told Insider it is important to clean reusable water bottles daily, using hot soapy water. A dishwasher is even better if it's an option, she said.

Anderson suggested using a small brush to clean the straw, pouring fast-running water through the straw, or leaving it to soak in hot water to encourage debris to come out.

But she said that if, like Houlihan, you find mold in your water bottle, it can be safe to continue to use if it is cleaned and sanitized properly, but this is down to personal preference, as some might rather throw it out.

"It's like if you have a cup of tea or coffee. You wouldn't clean it in a week's time," she said.

For more stories like this, check out coverage from Insider's Digital Culture team here.