The Collaborative International Dictionary of English v.0.48:

desensitizing \desensitizing\ adj.
   making less susceptible or sensitive to either physical or
   emotional stimuli. Opposite of sensitizing. [Narrower
   terms: numbing]
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

desensitizing
    adj 1: making less susceptible or sensitive to either physical
           or emotional stimuli [syn: desensitizing,
           desensitising] [ant: sensitising, sensitizing]