4. Apply antiperspirant to dry skin only. If your armpits are sweaty or if you've just gotten out of the shower, then dry your armpits with a towel or blow-dry them with a hair dryer set on a cool setting. If you apply antiperspirant to wet armpits, you may experience skin irritation. Use it on hot parts of your body. 2  This will moisten the skin so sweat won't have to. 3  Hyperthyroidism can cause too much sweating as a secondary outcome. 4  If you suffer from this condition then medical help is a must.