Lewis & Short

pustŭlo, āvi, ātum, 1, v. a. and n. [pustula].

  1. I. Act., to blister, to cause blisters or pustules; hence, mid., to blister, become blistered: ne usta pustulentur, Cael. Aur. Tard. 5, 1, 16.
  2. II. Neutr., to blister, break out into blisters, Tert. Hab. Mul. 6.