• Other cats roaming near the house can trigger spraying.cat image by Darren Ager from Fotolia.com
  
  A cat sprays when it backs up against a vertical surface such as a door, holds its tail high and sprays urine onto the vertical surface in a few short bursts. The cat stands tall and does not squat when it's spraying, as it does when it urinates. An adult male cat or an adult female cat in heat may spray to leave certain messages.
  
  

Territory

• A cat, especially an adult male cat, might spray to claim a territory. It can be a fixed behavior trait or a sign that he feels a territorial threat, such as new pets in the house or other cats coming near the house. Marking a territory with a cat's own scent gives him a sense of comfort and security. The cat might spray a door close to the house entrance where other cats or other outdoor animals have been.
  
  

Sexuality

• During the mating season, both male and female cats are likely to spray to communicate their availability using pheromones. They might spray on the door or the window through which they see possible mates.
  
  

Anxiety

• Spraying can be a cat's reaction to stress, anger, frustration or anxiety caused by factors such as a dirty litter box, lack of time spent with the owner or dislike of certain individuals. In this case, a cat may spray on doors just because doors have vertical surfaces.