Dr Christopher Callewaert is on a mission to develop a probiotic deodorant, a revolutionary product that promises to banish smelly armpits. Are we taking the microbiome theory a step too far, asks Donal O’Keeffe
‘Doctor Armpit’ is a nickname most might not fancy, but Dr Christopher Callewaert relishes it, even if it does call to mind a child’s idea for a supervillain. It’s Callewaert’s Twitter handle, his email address, and the name on his website.
Callewaert is a 32-year-old Belgian microbiologist whose field of research covers human bromhidrosis, or body odour, (BO), specifically the odours associated with armpits.
It’s an interest he says dates back to an “embarrassing” one-night stand when he was a 21-year-old student at Ghent University.
Callewaert’s work has put him on the cusp of scientific and possibly commercial success as he endeavours to develop a probiotic deodorant.
Key to Callewaert’s work is the concept of the microbiome, which has its own world day next Thursday, June 27. He quotes New Zealand microbiologist Mary Marples, who compared the ecology of our skin to an ecosystem: “The forearm is the desert, the scalps are the cool woods and the armpit is the tropical rainforest”.
According to Callewaert, there are two types of bacteria native to the human armpit: the ‘good’ kind, known as staphylococci epidermis, which don’t cause much in the way of odour, and the ‘bad’ kind, corynebacterium, which do, transforming lipids and amino acids in our sweat “into compounds which have a particular pungent odour”.
Most of us mask unpleasant underarm smells with deodorant, or with anti-perspirants containing an aluminium-based compound which temporarily plugs our sweat ducts. Both methods are part of a global industry worth approximately €20bn per annum. Callewaert may well be about to get a slice of that action. And it’s all down to his night of passion when he says, somewhat ungallantly, he “caught” BO from his date.
Callewaert’s horror at his own sudden change in underarm smell sent him searching for answers, and opened up a whole new line of academic work.
“The conclusion was that a microbiome transplant had happened to me. And if it is possible in the bad way, it also had to possible in the good way. I pitched the idea to a couple of professors, who liked it, so I applied for some grants, and that is how I got into this research.”
Catching BO, let alone curing it, seems an astonishing claim. Is this not taking the microbiome theory too far?
It is a great pleasure to be among these fellow armpit specialists at #skinmicrobiomecongress in Boston! With @NRCjulie and Gordon James from #Unilever. #SkinMicroCongress #skinmicrobiome pic.twitter.com/KNHqUoFVoa— Chris Callewaert (@DrArmpit) May 30, 2019
Callewaert disagrees, saying microbiome research is not even a decade old: “We are just at the beginning of finding answers to diseases that were previously unexplained. The root of the problem with underarm body odour is bacteria. I think it’s a valid approach to fight bacteria with bacteria, rather than with chemicals, which kill bacteria.”
Putting his research into practice, Callewaert says he has performed a successful microbiome transplant.
Asking the nice-smelling twin not to bathe for four days, Callewaert had the other twin wash with antibacterial products. Taking sweat from Mr Clean, Callewaert then applied it to the subject’s brother’s armpits using cotton swabs.After a second application, the former Mr Stinky’s armpits were as sweet-smelling as his brother’s, and he and Mr Clean were indistinguishable by smell.
Has humanity always been always been haunted by the worry of smelly armpits? Presumably, they were not much of a concern in the hunter-gatherer age.
“That I’ll soon find out,” he says. “I’m going soon to the Yanomami hunter-gatherers in the Amazon to sample their armpits.
“But yes, it’s a very old problem. But my gut feeling says it has become more abundant in the western world.”
There are many reasons we develop smelly armpits, Callewaert says. It may be an inherited problem, or it may be related to medical conditions, or result from the use of antibiotics, or perhaps from a hospital stay, or from the menopause, or from beginning or finishing birth-control medication. BO can also result from the over-use of antiperspirants or deodorants, or be due to a transfer of bacteria from dirty clothing.
“The use of antiperspirants specifically, containing aluminium salts, and to a lesser extent, deodorants in general, give rise to a higher bacterial diversity in the underarm,” says Callewaert.
“The bacterial density goes down, leading to less malodour, but you are left with a high diversity, and more stress-resistant bacteria, and as such also malodorous bacteria. The bacteria that come back can create a more unpleasant smell. With daily use and in the long run, this is not favourable.”
Armpits are an important part of the body, home to apocrine sweat glands and lymph nodes, and a moist, hairy and lipid-rich area host to many bacteria which can give rise to malodours.
Do men worry more than women about their armpits?
“It’s actually the other way around,” he says. “Women worry more about their smell than men. Although women tend to smell more pleasant and have less of the malodour-associated microbiome.”
Callewaert is the younger brother of twin sisters, one of whom died in a car accident when Chris was ten, he grew up on a farm.
“I was always surrounded by plants, chickens and so on. My parents made butter, grew salad, tomatoes and beans. As the only son, I was destined to take over the company, but I wasn’t a big fan of all the work.”
Studying biotechnical sciences in school, focussing on mathematics, biology and chemistry, he went on to study biosciences and bioscience engineering at university.
“Biosciences are the course of the future,” Callewaert says with passion.
He considers himself very fortunate to have received help with his research from so many people in Belgium.
“First, I sampled all of my colleagues at the lab at Ghent University, and many of my friends – that work was published in 2013 in (the Public Library of Science journal) PLOS One. Then, in 2013, Belgian media publicised our call for smelly armpits, which sparked the attention of 200 people who came to the lab.”
Callewaert says he has done extensive work involving “in vitro” techniques, but, in his experience, nothing is better than the real thing: a human armpit. The ethical committee at Ghent University approved his idea to perform armpit microbiome transplants, after he first carried out tests using in vitro simulation models.
He cautions that underarm microbiome transplants should not become mainstream, and mostly only help with severe cases of bromhidrosis. And he warns the process can include risks: potential pathogenic bacteria could be transferred, causing unwanted infections.
With one recent survey suggesting up to half of young men now shave their underarms, Callewaert says shaving the underarm brings a temporary improvement in underarm odour, but it is only temporary and “not significant”.
Is Doctor Armpit confident he can convince us to leave the highly scented sprays on roll-ons behind? “This is not my task,” he says. “Deodorants still work for most people. They do as they promise — they decrease the bacterial load and deodorise the armpit, adding a good perfume. Exactly what people want. But I think we can improve the product, by using the knowledge of my studies. Deodorants are a fairly young product, only becoming mainstream after World War II.”
Callewaert says he has already had meetings with some big cosmetic companies, and received some interest from potential investors, but will take his time to ensure he gets his formula right.
Given the annual global spend on deodorants and antiperspirants adds up to billions of euro, that perfected formula could be worth a lot of money.
So, no sweat, then.