You don't react the same way to everyone you meet—and neither do dogs. After all, humans come in all sizes, shapes, and personalities; it's impossible for any creature that's intelligent and sensitive (two characteristics dogs have in spades), to see us as being the same.
So why is it that one person might have your dog on his back cheerfully waiting for belly rubs while another might have your dog running in the opposite direction?
From a dog's perspective
Proper early socialization of a puppy is the best way to keep it from becoming unduly frightened of people. Since you may not have had control of your dog's early socialization and training, he may have been abused or traumatized by past experiences with people.
A dog that is frightened of people usually has his targets well defined and reacts strongly for a reason.
Size. People are generally larger than virtually any breed of dog, and dogs that are very submissive may have an adverse reaction to men with a large stature or a man with a really deep voice. This type of dog may see—and hear—the human as a powerful and, possibly, threatening entity.
Children. You may see children as cute and charming, but to a dog toddlers and youngsters may be perceived as unpredictable nuisances that don't know how to behave in a "civilized" and canine-appropriate way.
Strangers. People don't greet every person they meet with a big smile and a hug—and neither do many dogs. Like us, dogs often need to "warm up" to a person before they feel safe and secure with them. Then again, some dogs are so loving and eager to please, it seems like love at first sight.
Signs that say, "I'm scared"
Dogs that are fearful of certain people usually display predictable telltale signs. They may perform one of more of these behaviors:
- Avert their eyes
- Lower their head
- Sniff the ground
- Lick their lips
- Flatten their ears
- Tuck their body and tail
- Roll over to expose their underbelly
Does my dog need professional help?
As with humans, a certain amount of wariness when it comes to meeting new people is natural. However, a dog that is consistently fearful—and that reacts with strong fear behaviors/postures—may need professional help. This is common for dogs that may have been abused in the past. If your dog seems overly fearful and unable to shift into "trust mode," speak with your veterinarian about the best way to proceed.