There are several different reasons why dogs feel the need to immediately jump on people – both people they know and love and people they are just meeting. Reasons why dogs do this behavior include:
They are trying to say, “Hello!”
When dogs want to greet their owners or guests, they may want to jump up to try to get a closer look at them. They may be happy and have difficulty controlling their actions, and jumping up to come into better contact may feel as if it their only option.
They are excited to see someone
When dogs are excited, they want to romp and play. Jumping up on people is another way of showing that excitement. Excited dogs are not trying to be harmful by jumping up; however, it can hurt the person or even themselves.
People are taller than dogs, and they want to see their faces
Dogs are accustomed to meeting other dogs (or cats) by being at or close to eye-level. With humans, they may want to get a closer look at their faces so they can sniff and see them better. Jumping up is a way of getting closer to contact.
They feel the need for quick companionship
In order to get attention very quickly, dogs may jump up on their owner or guest to make it known. Dogs crave companionship, and when they have been alone at home for a while, the first thing they want to do is show their owner or guest they missed them while they were gone.