In the new study, the researchers divided 18 participants into three groups: those who regularly used antiperspirant, those who used deodorant, and those who didn’t use any products (the researchers distinguished antiperspirants and deodorants by their active ingredient). On the first day of the eight-day study, the participants continued their typical routines. For days two through six, they all stopped using those products. Then, on the last two days, all of the participants used an antiperspirant/deodorant product that the researchers gave them. Each day, the researchers took swabs from both of the participants’ armpits. They then cultured and sequenced the bacteria to determine how the microbiota changed over the course of the experiment.