Whether it’s summer or winter, we rely on it every day to stop our underarms from smelling of sweat. We roll, spray, or rub deodorant under our smelly armpits, but why do they stink in the first place and how do products work to mask the smell? In the latest video, “How Do Deodorants and Antiperspirants Work?”, the American Chemical Society’s Reaction series gets into the science of human body odor, focusing on the funky smell of our underarms.

Believe it or not, sweat is not smelly. Rather, it is the human microbiota — a collective group of microorganisms that lives on or in the human body — that comes in contact with what produces the odoriferous sweat, according to the ACS video. In the underarms alone, there are up to one million bacteria per square inch, making the armpit a factory for foul smells. The main two glands that produce sweat, known as eccrine (releases water and salt to cool us down) and the apocrine glands (releases a mixture of fats and proteins) come into contact with human microbiota to produce three primary odor compounds compared to the smell of goat, cumin, and onion, that carry the weight of the human body odor smell.

So how exactly do deodorant and antiperspirant stop these smells?

Deodorant targets bacteria by applying compounds like triclosan to kill or deactivate bacteria, while antiperspirants target sweat glands with substances like aluminum chloride compounds to give bacteria less nutrients to turn into gross smells. Currently, trioclosan is under rigorous scientific review by the Food and Drug Administration over its potential to alter hormone regulation and lead to antibiotic-resistant bacteria. Meanwhile, aluminum in antiperspirant has been linked to Alzheimer’s disease, but the scientific community considers this a myth.

Although these products are different, they both normally contain perfume and alcohol to sterilize the area well.