The best type of deodorant for sweaty armpits is a soft-solid formula over-the-counter antiperspirant. Deodorants by themselves do not prevent sweating but instead reduce odor-causing bacteria, while antiperspirants work to combat excessive sweat.
Applying an antiperspirant once before bed and once in the morning has proven to provide the best sweat-reducing results. Making sure there is no water or sweat on the skin prior to applying the antiperspirant reduces the chance of stinging and skin irritation. Before testing a new antiperspirant, it is best to use a small amount on an area of the skin to confirm that it will not cause a rash or irritation. It is also important to never wrap any skin in plastic, as this is sure to cause issues and provides no benefits at all.