Why does pepper make me sneeze?

A sneeze is a reflex action. Sometimes you can feel a sneeze coming on. But I think you cannot just decide you want to sneeze and then make a very good sounding sneeze.

Usually a sneeze is started by tickling or irritation of the membranes lining the inside of your nose. The sneezing reflex is useful in blowing out of your nose any dust particles causing irritation. Some substances, like pepper, contain chemicals that irritate sensitive membranes. Some of us are more sensitive than others. I guess you and I are among the more sensitive ones.