Many people express disgust or surprise when they see their dog eat dirt, but this action is actually commonplace amongst many dogs. While not every dog will eat dirt, many will given certain situations. If you notice your pet eating dirt, it's not necessarily a bad sign, but it may be. Keep a close eye on him to watch for other telling behaviors that can show you that he's eating dirt due to an underlying medical condition that you need to address.
Mineral Deficiency
One reason that some dogs eat dirt is because their standard diet lacks in certain minerals. If this is the case, your dog may revert back to his instinctual tendencies to try to obtain the rest of the important vitamins and minerals that he needs in order to survive healthily. If he isn't getting the minerals he needs from food, he may try to get them by eating dirt. Check if your pet eats dirt frequently when he's outside; if he doesn't, this is a potential sign that he may be missing out on certain materials that he needs for his diet.
Check on his dog food label and compare it with a list of important minerals and vitamins that all dogs need. You can find this list online in a variety of different sources. If the food is missing many of those crucial vitamins and minerals, get rid of it and purchase a higher quality and well balanced food for your dog. Generally, this entire problem can be avoided if you purchase a good quality dog food product for your dog at all stages in his life.
Gastric Upset
In other situations, a dog may begin to eat dirt if he has already eaten something that has begun to upset his stomach or his intestinal tract. Eating dirt is an attempt to dilute or to get rid of the offending food item. This may be something as mild as a plant that has caused him a bit of distress, or it could be something very serious, like one of several human foods which are poisonous to dogs. Watch for your dog eating dirt one time only but for a sustained period of time. If he eats a lot of dirt at once, this is also a potential sign that something is the matter with his bowels or his stomach.
Minor Issues
In many other situations, your dog will appear to be eating dirt but may actually be eating some food item that lies in the grass or on the ground. in these situations, the dog will likely not eat very much dirt at one time and it will only be a single occurrence. Keep in mind that your dog can smell food that is buried under the ground significantly better than you can.