Your dog's hair growth cycle
In contrast to the normal situation in human hair growth, most dogs have a coat of hair which is in a constant and very active state of turnover. Some dog breeds such as Poodles and Bichon Frises have a more similar growth cycle to humans as they do not shed very much, instead retaining their hairs which are in the resting phase of growth for a prolonged period.
Your dog's coat consists of a mixture of long primary and shorter secondary hairs. The proportion of each type of hair will vary depending on age and breed, for example puppies usually lack primary hairs, having only the softer secondary coat. The cycle of hair growth consists of the anagen, catagen, and telogen phases. During the anagen phase, the dog's hair follicle is actively forming a new hair which grows alongside the old hair, eventually forcing it out to be shed. Telogen is the resting phase, when the hair follicle is inactive, with catagen representing an intermediate phase. Much of the detail of the growth cycle is only vaguely understood, one of the reasons why baldness remains a difficult problem to solve, both in humans and animals!
Although your dog is losing hair on a continual basis, the hair follicles are normally not all in the same phase of growth, so it is unusual for generalised alopecia or baldness to develop.
Dogs shedding hair excessively
In many cases, deciding whether a dog is shedding excessively is a subjective judgement, based on owners seeing a lot of hair coming away while grooming, 'tumbleweeds' of hair around the home, or matting of dead hair in the coat. However, we may objectively say that a dog is shedding excessively or inappropriately when hair growth is unable to keep up with hair loss, resulting in baldness.
If your dog develops areas of baldness (alopecia), you need to assess whether there are any other symptoms which might suggest an underlying medical cause for the problem. Symptoms such as weight gain, lethargy, or excessive thirst may be suggestive of Cushing's disease or hypothyroidism for example. Dogs displaying systemic signs such as these should certainly be assessed by your veterinarian.
Hair loss in a dog due to Cushing's disease
Excessive shedding associated with itching
If your dog is losing a lot of hair and also displaying signs of itchiness, it is important to rule out inflammatory skin disease. This may be caused by parasites (eg fleas, mites), bacterial and fungal infections, skin allergy, folliculitis or immune mediated disease (eg sebaceous adenitis). The good news is that these are treatable diseases. While some may potentially require lifelong treatment, others such as parasitism may be treated simply with an over-the-counter topical skin treatment. Any dog that is losing hair and scratching should be treated for parasites at an early stage in the investigation. A dog that continues to scratch even after parasite treatment will certainly need to be seen by a veterinarian for investigations such as skin scrapings, fungal cultures, and sometimes biopsy.
Other causes of baldness in dogs
There are a staggering number of other possible causes of hair loss in your dog. Several of these are caused by or responsive to sex hormones such as estrogen and testosterone. Pregnant or lactating females very often develop areas of alopecia as a result of the hormonal changes in pregnancy. Even neutered animals can develop problems of the adrenal glands which can cause the production of hormones normally associated with the ovaries or testes. A dog losing hair belonging to a breed such as a Chow Chow or Pomeranian may be suffering from growth hormone-responsive alopecia.
From a veterinarian's point of view, diagnosing one of these endocrine causes of baldness in dogs can be costly and time-consuming, as with few exceptions, they all appear similar clinically. On behalf of all the vets out there, please be patient as the multitude of tests is being conducted!
One of the most common of these miscellaneous causes is seasonal alopecia. It typically affects dogs during the months of shorter daylight hours (Fall to Spring), and can last up to 6 months. Boxers are particularly prone to this problem. Although it is not always responsive to treatment, a treatment trial with melatonin (usually 3mg twice daily for an average sized dog) over several weeks may result in hair regrowth. Even without treatment, a dog that has lost hair as a result of seasonal alopecia will usually regrow his normal coat in the Summer.
Melatonin 3mg tablets
Omega 3 supplement
What to do if your dog is shedding excessively but not developing baldness
For those dogs described above with a full coat of hair (ie no patches of alopecia), there are some options to reduce 'nuisance' shedding. Regular grooming is important to both help remove loose anagen hairs in a controlled fashion, as well as stimulating blood flow to the hair follicle to encourage healthy hair growth. The Furminator is a great product for stripping dead hairs from heavy shedders. It is a huge favourite with the groomers in my clinic as it reduces their workload if the dog's owner has been using it at home!
Dietary supplementation with omega 3 fish oils also helps with healthy hair growth and coat retention. There are diets available which have been supplemented with omega 3 such as Royal Canin's Skin Care diet, but for others the addition of supplemental oil may be helpful.
Extremes of temperature may encourage continuous heavy shedding. Dogs which live both indoors and outdoors are often the heaviest shedders. There may be no easy solution for this without changing the dogs lifestyle to an unacceptable degree, and unfortunately as dog lovers we sometimes have to live with the odd tumbleweed!
My last suggestion would be to invest in a good vacuum cleaner if all else fails....