Having a pet in your home can significantly improve your mood since whether you have a cat, dog, parrot or snake you know that you have a creature for company who makes you feel less stressed and takes away the loneliness. Dogs and cats can be particularly effective at improving your mood, as they are tactile creatures, and when you're stressed it is nice to be able to stroke your pet and for this to elicit some kind of response. Your dog may start to lick you or your cat might begin to purr and so this exchange is a two-way process. You have interaction without having to worry about what anybody else might be thinking.
Animals are a lot easier to cope with than people, and you know that whatever you do, they will love you without judging you or your actions. Pets can stave off loneliness and thus the depression that accompanies loneliness. Knowing that your pet is waiting at home for you can improve your mood, as you actually have a purpose. When you get home you may have to walk your dog, as well as feed it, and he may want to play a game, so that you don't get home and start to focus on how bored and lonely you are.
If you own a dog then you will have to take him outside for his walks which can benefit both your physical and mental health. Exercise promotes the release of chemicals that make you feel good, reducing your stress and anxiety levels, while reducing negative feelings. You will also improve your physical health by giving your heart and limbs a workout, while maintaining a healthy weight will be easier, thus giving you one less thing to worry about. Walking your dog also provides you with an opportunity to engage with other dog owners, and if you are quite isolated and depressed, this social interaction can improve your mood.
No animal is the same, and they each have their own personalities. You get to learn their likes and dislikes and they become part of the family. There are some downsides to owning a pet, such as when they become ill and you have to pay exorbitant vets' fees, but the benefits far outweigh any disadvantages. Most of the time your pet will manage to improve your mood, but you become so attached to them that when they finally leave this world it can be devastating. However, you get so much out of owning a pet that in the end you usually find it impossible to live without one.