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Activated charcoal is made by heating unactivated charcoal to a very high temperature in the presence of an inert gas.
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Professor Ian Shaw, director of biochemistry and professor of toxicology at Canterbury University, said this process creates lots of pores in the charcoal, which makes it have a very, very high surface area.
"The chemistry of the charcoal enables it to bind to many, many different sorts of molecules and with this huge surface area, it can bind a very large amount of chemical material. So if you put some charcoal into a liquid, for example, that might have some chemicals in it, then the chemicals will bind to the charcoal and remove them from that liquid."
"It looks like the Phoenicians in around about 400 BC actually made activated charcoal by heating charcoal in a fire to very high temperatures. And they use that powdered activated charcoal to purify their water," said Professor Shaw.
And for many years toxicologists have used charcoal as a treatment for poisoning.
"So, the whole trend around this whole activated charcoal movement is basically it stems from the fact that in medical settings, activated charcoal has been used to treat overdose of drugs and poisoning and things like that," he said.
But Dr Rajshri Roy says the idea of charcoal as a detoxifier has been hijacked by the food and beauty industry.
"So our body has organs that take care of the detoxing process. No particular food helps with detoxing. Your kidneys are going to do that, your lungs are going to do that, and your liver is going to do that," she said.
And Professor Shaw goes even further.
"I'm really unhappy about just adding something that indiscriminately binds to so many things on the grounds that it will stop you getting exposed to toxic chemicals in your food," he said.
"If you eat activated charcoal, it will bind lots of things to it. Some of those things might be nasty chemicals that might be in your food like pesticide residues, for example, that would be present in tiny, tiny concentrations. We wouldn't even call them toxic at those levels, but it will also bind other things from the food which might be useful. For example, some of the vitamins might bind to charcoal and some other micronutrients might bind to charcoal."
"For people who are on prescription medications, the activated charcoal could prevent the medication from being absorbed properly as well. And the thing that we did some research on around oral contraceptive pills, for example, like if you're having that and you're also having a lot of activated charcoal, the potent agent could not be absorbed into your system," said Roy.
She said if people are having small amounts, there's no harm to it - but there is no benefits either.
Apart from food, activated charcoal is being used more and more often in beauty products
But Professor Shaw is pretty skeptical about the actual benefits of this too.
"If you covered your face with a charcoal-containing face pack, it will bind to all sorts of stuff on your skin. And I suppose you could say it's going to help you to detoxify your skin. But I must admit, I think that's pushing it a bit," he said, "Because the amounts of material concerned in the skin will be very small, it'll only be dealing with things actually sitting on the surface of your skin. So I think there might be a bit of advertising benefit there rather than any reality."
Toothbrushes and toothpaste
"Certainly charcoal can be abrasive and so just like other products that are used to brush teeth, there is often an abrasive component, and it can help remove deposits on the surface of teeth."
But he said: "If the particle size of the abrasives is large or if it's used particularly aggressively, you can also abrade the tooth itself which something you don't want to do. Because teeth are a part of your body that can't rebuild itself once damaged once missing, the tooth surface is stripped away is gone for good,"
And he said if you're not dealing with the cause of the staining in the first place, your teeth will soon revert back to the pre-brush colour.
Dr Broadbent also said charcoal’s ability to bind to anything, good and bad, is a problem in toothpaste too.
"There is suspicion that in a charcoal containing toothpaste that fluoride would be less bioavailable than it would otherwise be," he said, "There's worrying lack of actual research to verify this one way or another."
A 2017 review of charcoal in dentistry products, published in the Journal of the American Dental Association, found there was no good evidence that charcoal is effective or even safe for teeth.
Broadbent also suggests it could make them look worse.
"If you've got early decay on tooth surfaces, where the tooth surface is slightly demineralised, it can either be abraded away or stained up by a charcoal infused toothpaste," he said.
Listen to the full podcast to hear more about charcoal and find out what host Stacey Morrison and her seven-year-old daughter Maiana thought about their test run with charcoal dental products.
Some of research papers reviewed for this podcast are below.