You may notice that some dogs have a tendency to lick things constantly. Licking behaviours derive from a variety of reasons and causes, which can be explained based on what it is, exactly, that the dog is licking. Pay attention to the types of materials your dog is licking to see if you can figure out why your dog wants to keep licking it.
A dog will lick -- and sometimes chew -- its paws if it is suffering from allergies. Dogs can have allergies to certain types of foods, such as corn and grains, or dogs can also get allergies from pollen and dust outside. Excessive paw-licking is one of the main symptoms that veterinarians look for when they are diagnosing a dog with allergies.
If a dog licks you on your hand or your face, giving you "kisses," you may have rewarded him once or twice with physical and verbal reinforcement, such as a hug and a "good boy." It is possible that your dog, in fact, learnt that licking and affection leads to positive rewards, and so it will continue to lick, lick, lick. This behaviour will go beyond just hand- and face-licking, and can manifest into licking other things as well, including other people.
Your dog can taste salts, sweet lotions and other things that you leave behind from your hands and body. If you put lotion on your feet and walk across the tile floor, you might expect to find your dog following behind you, licking the tile. This is because it tastes the lotion and is interested in it. Similarly, you might catch you dog licking the kitchen floor, refrigerator door handle or cabinets if you have spilt something without noticing.
Your dog might lick everything in sight because it is lacking something from its diet. A vitamin or mineral deficiency can cause dogs to lick concrete, bricks, rocks and other materials. If you notice that your dog is constantly licking things, check the ingredients in the dog food and make sure your dog is getting enough daily recommended vitamins and minerals. You might need to change the dog food or get supplements for your furry friend.