The first step to stopping sweating under your arms is to make sure you are wearing the right size shirt. You’ll need a shirt that has a generous scoop neck and close-fitting arm holes. A large sized man should wear a medium or large, while a woman will want her large shirt to fit snugly without being too tight. This helps eliminate excess moisture from building up underneath your arms.
You also have to avoid using anti-perspirants that contain aluminum chloride or antiperspirants with aluminum zirconium. They can cause skin irritation which will only worsen as time goes on if left untreated, so use them sparingly at most – just enough for those few days when you have an event where it would be appropriate for you not to sweat so much!