The term comes from Greek kyōn, a kind of dog, and phobos, fear. The English word cynophobia came into use in the early 19th century; before that time it was usually called ‘canine phobia.’
It is one of the most common phobias, and affects about 10% of people. There are many possible causes: fear of being bitten or attacked; a traumatic experience associated with dogs in general or a specific dog; guilt about hurting a dog when it was young; dislike for how they smell. People who are phobic about dogs may avoid them for fear of being hurt, even though they know they tend to be friendly. They may freeze or feel nauseous when confronted by a dog.
The majority of dog bites are from unneutered male dogs and we know that neutering will stop this. In addition, humans have evolved to interpret certain facial expressions as ‘angry’ or threatening (e.g., a bared set of teeth).
Cynophobia is a common fear among children. They often cannot overcome their fear as adults, although sometimes cynophobics become dog owners themselves.
Interestingly, it seems that’s not the only phobia of dogs. There is also a fear specific to small dogs, called ailurophobia (from the Greek words for cat and dread). Some people are afraid just of black dogs.