Very often, anxious dogs have difficulty accepting the arrival of someone they don't know. In this case, fear and stress are the main causes of a number of behaviours which may appear rather aggressive, such as excessive barking, growling or baring their teeth, or rather fearful, such as cowering, keeping their tail between their legs or having their head very low. Not all dogs react in the same way when confronted with fear, but in general they will always try to keep a certain distance between the source of the fear, i.e. the new person, and themselves.
When introducing a new person to a dog, it's important to create a calm, positive experience for all concerned. Ideally, when time and space permit, it's best to choose a neutral environment where the new person and dog can meet. A good example: take a walk outside with your dog and introduce the guest to the dog during the walk, simply by walking the person next to you. The dog will then be able to get used to the person's presence and voice, while being distracted by his surroundings, in an environment he doesn't consider familiar.
An introduction can also take place in a home, but it's important to understand that your pet's attention will then be completely focused on the new person, which may elicit stronger reactions from your dog. To begin with, ask the person to remain relaxed and let the dog come to them. Avoid sudden gestures or frontal approaches, as these can frighten the animal. Encourage the person to crouch gently to appear less intimidating, and to hold out an open hand for the dog to feel. If the animal is still too frightened, the person can also turn his back to the dog. When the dog shows signs of comfort, such as wagging its tail or coming closer, the person can try stroking it gently under the chin or on the side of the body, rather than on the head, which can be perceived as invasive.
Finally, pay close attention to the dog's body language: if it seems tense or nervous, give it more time to get used to the presence of the new person. A stressed dog may show the following body signals: a rigid posture, dilated pupils, visible eye sclera, a fixed or evasive gaze, ears flattened backwards and a tail above the line of the back or a tail tucked between the hind legs. Remember, patience is always the key when a dog is suffering from anxiety!