When your dog has a relaxed mouth, corners drawn up, and “soft” eyes, he really is smiling at you! As with humans, dogs communicate a lot of information with their facial expressions.
A furrowed brow indicates worry or attention, wide eyes indicate excitement or fear, narrow eyes indicate anger, etc.
Different dog smiles can mean different things. A gentle smile with relaxed lips, eyes, forehead, and ears is what we would consider to be a genuine smile, indicating affection and ease. Open-mouthed smiles with alert eyes and ears can indicate excitement over a favored item (toy, leash, treat) or situation (such as a game).
Smiling with a closed mouth and alert eyes can be an indication of mild stress (pulling away slightly from another dog considered too close for comfort, for example), and is sometimes interpreted as an expression of distaste. A closed-mouth smile with slightly bared teeth is a warning, whereas an open-mouthed smile with teeth showing is a sign of submission. If the lips are pulled all the way back and the teeth are bared, the dog has reached the threshold for aggressive behaviors, stemming from extreme anxiety, fear, or frustration (anger).
Learning to identify your dog’s full range of smiles can help you to better understand his emotions.