Most anti-perspirants contain a gel-like ingredient that works to reduce sweat from the skin. It does this by covering the ducts and pores we sweat through – forming a protective layer, in a sense. This can last for several hours, so less sweat escapes through your skin. With time, this protective layer dissolves and the skin sweats as it normally would until more anti-perspirant is applied.
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You are what you eat - the odour of your sweat can be affected by the food you ingest - garlic and curry are notorious examples!