The Collaborative International Dictionary of English v.0.48:

Irritative \Ir"ri*ta*tive\, a.
   1. Serving to excite or irritate; irritating; as, an
      irritative agent.
      [1913 Webster]

   2. Accompanied with, or produced by, increased action or
      irritation; as, an irritative fever. --E. Darwin.
      [1913 Webster]

WordNet (r) 3.0 (2006):

irritative
    adj 1: (used of physical stimuli) serving to stimulate or
           excite; "an irritative agent" [syn: irritating,
           irritative]