Fur loss in a dog is known as alopecia.  It is common for the cause to be an allergy; whether a food allergy, environmental allergy, or parasite allergy.  It can happen anywhere on the body at any stage of your dog’s life. However, allergies are not the only cause and we also have to consider e.g. endocrine disorders, fungal infections and mange.

If you are able to determine the cause of the allergy, his treatment process will be more successful.  Keep in mind if you do not treat his thinning hair coat, it is likely to worsen and spread to larger regions of his body.

It is normal for your dog to shed some fur, but it is not normal for him to lose large amounts to where his fur is thinning or even bald.  If your dog’s coat is thinning or balding, take him to his veterinarian for an evaluation.

Symptoms of this condition may include:

Hair loss can happen at any location on the body.  Flea allergies typically start out by causing fur loss on the hind end which slowly works its way up the trunk to the rest of the body.  If it is from a contact allergy, the fur loss will most likely originate where your dog comes into contact with the item.  For example, if he is allergic to the grass, his feet will itch first.  This will cause him to chew at his feet to where he eventually chews off the fur.  If it is a food allergy, the most common starting point of fur loss is the belly, face and paws.

Hair loss in your dog from an allergy can be from one of many things.  One very common cause is flea allergic dermatitis. This is when your dog is allergic to the flea saliva. When the flea bites your dog, it causes intensive itching and therefore scratching.  The scratching and irritation cause the hair to fall out, leading to your dog having a sparse hair coat.

Another common cause is atopic dermatitis.  This primarily causes the skin to develop scaly, itchy patches which affect the fur as a result.  Your dog will chew and scratch himself to where he scratches off his fur.  Also, if the skin is unhealthy, it does not produce as healthy of a fur coat as usual.  Atopic dogs react to a range of triggers including certain foods, dust mites, pollen and grass.

Of course a food or environmental allergy can also cause your dog to lose his fur.  A food allergy can develop slowly over time so that you do not associate your dog’s hair loss with what he is consuming.  It may also develop years after being on the same food so many people do not believe this to be the cause, when in reality it is.  Environmental allergies can also affect your dog when he comes into contact with it or by inhaling it. Allergies tend to develop between the ages of 1 and 5.

When you arrive at the veterinarian’s office, she will start her diagnostic process by collecting a verbal history from you.  She will want to know when you first noticed your dog was losing his fur, if and where he has been scratching or licking excessively, and if you have tried to treat it with anything over the counter or not.  As part of her diagnostic process, your veterinarian will need to rule out other possible causes that can produce hair loss with similar symptoms like the one he is presenting with.  She will also want to know if you have fed him anything new lately, if he has had any changes in his routine or home that could cause stress, or anything else information wise that may be helpful to know about his situation.  

Your veterinarian will then continue by performing a full physical exam on your dog.  While it may be obvious where the fur loss is occurring she will want to do a full evaluation of his entire body system.  This will allow her to check for other areas of fur loss or skin abnormalities. During her examination, she will watch for signs of itching or the need to scratch from your dog.  She will check for evidence of parasites, palpate his joint and muscles, and give him an overall evaluation.  

Your veterinarian will come to her diagnosis by ruling out other possible causes of his symptoms.  There are similar conditions that can results in fur loss.  Diagnostic tests the vet may perform include skin scraping, skin cytology, blood work, allergy testing, and a check for other parasites.  A skin scraping will be done to rule out skin mites.  Skin cytology and swabs/plucks can rule out a bacterial or yeast overgrowth of the skin that can lead to loss of fur.  

During her examination, if there is evidence of fleas or other ectoparasites, she may explain why this may be causing his symptoms. However, dogs with flea allergy dermatitis do not necessarily have to have fleas on him for him to have a reaction.  It takes only one bite from a flea to start your dog’s symptoms.  It is possible a flea jumped on your dog, bit him, jumped off or died, and therefore you do not see fleas on him.  But it is too late; the flea bit him and therefore the flea saliva is causing your dog to have an allergic, overly sensitive response to it.  This is extremely common to see and therefore many owners find it difficult to believe their dog’s symptoms are from fleas. 

For environmental and food allergies, intradermal and blood testing can help us diagnose the allergen, though these tests aren't always reliable. For food allergies, the main way to come to a proper diagnosis is a trial and error dietary study; it is known as an elimination diet trial.  You remove the suspected allergen from your pet’s diet for a minimum of 12 weeks.  This gives his system time to remove any remaining ingredient completely and hopefully his symptoms will begin to resolve.  

Gastrointestinal signs typically resolve between 1 to 3 weeks.  Dermatologic symptoms take much longer to resolve as it takes the skin time to heal.  If his symptoms have resolved during this time, you need to reintroduce the suspected food item to get a confirmation.  If you offer the suspected allergen to your dog again and his symptoms reappear almost immediately, you have your culprit.

Ideally, the best treatment involves treating the region of hair loss, breaking the itch cycle, and removing the underlying cause. If you do not break the lick/scratch cycle, your treatments will be useless.  You must stop the need to lick and scratch in order to break the cycle of fur loss and resulting issues.  You must also address the underlying cause.  Your dog may stop licking for a while, but if there is an underlying cause, it is only a matter of time before he begins again.  

If this condition goes untreated, your dog may develop papules or pustules around the areas of fur loss where he continues to scratch and lick.  This is a sign of a bacterial infection and would need antibiotic therapy in order for it to heal.  If this is the case with your dog, the veterinarian will send you home with a prescription of an oral antibiotic.  Medications to be applied topically to the lesion may also be sent home depending on your dog’s needs.  

If ectoparasites are the cause of his symptoms, your veterinarian will suggest a type of flea prevention or other medication to take care of the parasites.  You will also need to make sure you treat your home, other pets and yard for fleas to prevent them from bothering your dog.  Be sure to vacuum regularly, wash any bedding your dog uses, and keep anything he regularly comes into contact with clean.

If your dog has a food allergy causing his fur loss, remove it from his diet.  If it is an environmental allergy, there is immunotherapy available in the form of shots or sublingual drops.  Administering these medications can slowly teach your dog’s immune system to not react so severely to the allergen.  Given time, this will allow your dog to not scratch from itching and therefore his fur will grow back.

If you are able to determine the source of your dog’s allergy and remove it, he should recover nicely.  However, if you do not remove the source, your dog will continue to lose fur and probably worsen.  Finding the cause may be tedious, but it will be best for you and your dog in the long run so that treatment is successful. Flare ups require medication as needed.