No matter how often you apply or spray a deodorant, it won’t lose any of its effect. That is what VRT science journalist Koen Wauters found out after investigating a query from Wouter Landuyt, a VRT listener from Ghent who put this question to the VRT’s consumer team on "De inspecteur" (The Inspector).
Wouter had been convinced that after long-term use, deodorant loses its effect. "But that is just in Wouter's head and not under his armpits," says Koen Wauters. So how does deodorant work and why do we sweat?
Wouter has the habit of using different deodorants switching from one to the other. "I start with a roller stick, then alternate with a spray and then switch to a cream. Because if I use the same deodorant for too long, in the long run it no longer has any impact. Then I start smelling more like sweat again. So I suspect that after a while, deodorant doesn't work as well. Is that right?"
Science expert Koen Wauters isn’t having any of this: "Sorry Wouter! There is no evidence that deodorant gets used to your skin and therefore stops working after a while. It's all in your head and not under your armpits."
However, you may eventually stop smelling your deodorant because your senses get used to its smell. "Just like rubbish collectors don't smell the smell of the rubbish either in the long run," he says.
How to choose a good deodorant?
So you don't need to switch deodorants. But how do you choose one that works well? "Deodorant is a combination of alcohol with a fragrance and sometimes salts. Some deodorants mention 'antiperspirant' (or in Belgium antitranspirant) on the label: then they have salts added to them that start blocking the pores in your skin and no or less sweat comes out of your body."
However, research shows that antiperspirant makes bad bacteria survive even longer. "So it's better not to use those. Most people don't need them either, just people who suffer a lot from streaming armpits."
What about the choice between roller and spray? For our health, it makes less difference. But bacteria can infect a roller more easily than a spray. The latter does not come into contact with your arm, but still has disadvantages: it is less efficient because you spray a lot next to the place where it is needed. Moreover, a spray also contains propellants that you inhale. Some people can have an allergic reaction to these. Also bear in mind that sprays also trigger more allergic skin reactions than with a roller.
More than 100 species of bacteria live under our armpits, feeding on sweat that starts to smell
Less stress, less smell
It’s not advisable to use your deodorant 4 times in a day. Use it in moderation and combine it with healthy eating. Research shows that lots of vegetables and less meat help against excessive sweating.
Avoiding stress also helps, as stress stimulates the apocrine glands. Your choice of clothing can also make a difference: cotton clothes are less likely to make you sweat than synthetic fabrics.
Types of sweat: from onion to stale
Fresh sweat doesn't smell, but the bacteria living in it do. More than a hundred species of bacteria live under our armpits, together forming a microbiome. They will feed on that fresh sweat and what remains of it will stink.
Each bacterial species also gives off a certain, specific smell. So one time you might smell sour, another time like onion or just a bit musty. This balance is obviously different for everyone: some people smell of sweat faster than others. That's just the way it is. It is that microbiome that determines whether you smell more or less.
We stink more since we’ve been using deodorant
In fact, recent research shows that since we have been using deodorant, for the past 50 years say, the bacterial culture under our armpits has changed, but not for the better. In fact, the bacteria that produce a bad smell seem to survive best!
Another fun fact is that smell is genetically determined, by the same genes as our earwax. And so it is that Europeans smell more and have yellow, moist earwax, while Asians sweat less and have white, dry earwax.