Thin Skin, Thick Hair & the Canine Immune System

All groomers are essentially topical dermatologists; we work on the outside of the dog to clean, condition, and routinely care for the skin and the hairs that grow out of it. And I know I am not alone in wishing that some basic canine skin and coat education could be required of all professional dog groomers… 

Veterinarians often report that skin issues are the most common reason for patient appointments, other than routine annual examinations. A veterinarian’s medical function is to work on the inside of the dog—including disorders of the skin—and our job as groomers is the routine care of the outside of the dog; the skin and coat. 

Some groomers even go on to become Canine Estheticians, which means they are able to do non-medical therapies for skin and coat issues. Esthetician expertise requires significantly extra (but invaluable) training, but it’s a great enhancement to any groomer’s business.

Dogs, like humans, are mammals. One definitive feature of all mammals is that we have skin consisting of multiple layers with impressively complex functioning. All mammals also have pores in their outer skin layer, or epidermis, that open down into hair follicles located in the dermis, which is an inner layer of the skin. 

Hair length in grooming matters to the health of the skin. It is not an understatement to say that perhaps the most hotly debated topic on groomer social media is how long or short certain kinds of haircuts should be for specific breeds. As with any complicated question, the answer is generally, “it depends.”

DOGS VS HUMANS 

Since skin is the largest and most important organ in any mammal’s body, it helps to consider how dogs are different from the skin we know the best—our own. The thickness of the skin itself and the amount of protective covering such as hair, feathers, scales, etc., for any species, is generally inversely related. 

Our skin is much thicker than dog skin. And we have much less hair, as far as mammals go, than dogs. Dogs have much thinner skin and many more hairs and hair follicles. Yes, there are the very rare hairless dog breeds, but all other dogs, on the outside, are mostly hair and we are mostly skin. We have thick skin and thin hair, with one hair per follicle and not many follicles. Dogs are the opposite; they have thin skin and a lot more hair, with many hairs per follicle and lots more follicles.

There are many vital functions that skin and hair provide to both people and dogs. Skin stores nutrients, aids in hydration, regulates temperature and a long list of other important benefits. Most importantly, skin and hair provide protection from external toxins, abrasion and other dangers in the environment. The skin is a barrier that protects our vital organs inside. The hair on a dog is the barrier that protects the skin. This is why many skin and coat educators do not recommend balding a dog, even in its groin area underneath the torso. I recommend no shorter than a #5F on the groin, leaving some protective hairs on very thin skin. 

CONSIDERING THE COAT TYPE

When trying to evaluate the optimal length of a haircut for protecting a dog’s skin, we should remember that, for the purposes of discussion, we are only talking about dogs that are “hair-type,” or UDL (genetically undetermined length hair). Like the hair on human heads, UDL hair grows and grows until it is cut or breaks. “Fur-type” dogs are shedders with genetically pre-determined length hair, or PDL. Like the hair on our arms and legs, it should not be cut, just de-shed. This is especially true for the upper torso or jacket area where the sun hits the most directly.

It is not surprising that our customers are not aware of this distinction. They will commonly ask for their dogs to be shaved down or given a “summer cut” without regard to the type of coat or its vital function. This is why it is so important for groomers to be well-versed in the different coat types and be prepared to gently educate the customer to do what is best for the health of their beloved companion.

LANGERHANS CELLS

In 1868, a German physician and expert in anatomy named Paul Langerhans discovered the cells in the skin that bear his name. Later, these vital cells were found to be a central part of the body’s immune system; a complex network that helps the body fight disease. Langerhans cells are key to the skin’s protective function. All mammals have these cells in their skin, and they are a very important part of our immune system. 

Many research studies have been published on the critical work of the Langerhans cells in mammals, including humans and dogs. The National Institutes of Health website, among several other sites easily found on internet searches, contains medical findings that connect problems that can develop in canine Langerhans cells with cancer.  

Now for some medical jargon: One example of a study published in the National Library of Medicine about the relationship between sunlight and canine skin cancers states, “Tumors developed in lightly-pigmented glabrous following chronic sunlight exposure…Microscopic examination of tissues from three dogs showed progressive development of epithelial hyperplasia through stages of solar keratosis-like lesions to invasive and metastatic squamous cell carcinoma.” 

Translation, please??

Basically, in English, Glabrous is a kind of mammalian skin with no hair: Think palms of your hands or a dog’s foot pads. Epithelial refers to skin. Hyperplasia is when organs or tissue, in this case, the skin, see an increase in the reproduction rate of its cells, also a common precursor to cancer. Solar keratosis refers to precancerous scaly spots found on sun-damaged skin. Squamous cell carcinoma is the second most common form of skin cancer. 

Several studies on the effect of sunlight on Langerhans cells find, in short, that if sunlight reaches a dog’s skin, it destroys Langerhans cells or causes them to become cancerous, just like it does on our own skin. It is especially impactful on dogs’ skin because their skin is much thinner and their lives much shorter. But they have their extra number of hairs and follicles to protect them, right? This is where the groomer’s role becomes critically important in the life of a healthy dog. 

WHAT THE INDUSTRY EXPERTS SAY

The educator whose teaching first inspired me about the importance of grooming for the health of the canine skin and coat was Michelle Knowles, ICMG, MPAe. Her classes were a game changer in my grooming career. She says, “The very foundation of what we do starts with a healthy skin that grows healthy coat. Learning the concepts of the skin processes and how they are affected by tools and products is essential for maximum health and a successful career.”

Dr. Cliff Faver is a gift to our grooming industry when, let’s face it, many veterinarians do not regard us as professional peers or partners. A career veterinarian with expertise in diagnosing and treating skin problems in dogs, Dr. Faver teaches grooming seminars about how dogs’ skin and coat work, and the techniques and products that are most helpful to each skin and coat type. He also offers advanced training for groomers in non-medical therapeutic approaches that we can use for problem skin and coats. When asked what length haircut is best to protect a dog’s skin, he recommends a minimum length of approximately one inch. But he is also clear that there are no published studies yet to offer specific set lengths, so this is just a generalized guideline. 

Linda Easton, ICMG, who runs International Professional Groomers (IPG), has also had a long and distinguished career showing dogs. She teaches regularly about the importance of protecting dogs’ thinner skin and vital Langerhans cells by leaving some protective-length coat. In dogs that receive haircuts, Linda encourages groomers to evaluate the individual color, texture and thickness of the coat when deciding length, but recommends no shorter than a #4 blade. If the coat is thinner and lighter in color, more length is needed for the coat to protect the skin.

THE DETERMINING FACTORS

The reason that there is no one exact length shorter than which groomers should not go is because there are so many variations of texture, thickness and coloring in dogs’ vastly varied coats. Grooming is not “one size (or cut) fits all.” Good groomers differentiate their grooming based on that dog’s coat type. Artistry aside, to prevent skin cancers and other health concerns, we must first work to protect what the dog’s coat does for its skin.

The first guiding principle regarding protective length of coat should be to know that only hair-type dogs (those with a UDL coat) should be trimmed at all—especially on the upper torso where the sun hits the most. This is not the case for fur-type (PDL) dogs. 

But how short can you go? 

The study cited earlier referred to “lightly pigmented” skin as being more at risk. This is true for humans as well. So, a good rule for haircut length is, the thinner, the lighter, the longer. Thinner hair protects skin less; lighter-colored hair protects skin less; therefore, more length is the most protective. 

Another helpful rule is, leave as much hair as you can. Groomers are in the coat preservation business, not the coat destroying business. We all must work with owner-length preference and grooming schedules. We all battle the effects of weather and puberty on a dog’s hair, which can vary the lengths we have to cut. 

The one-inch recommendation would be important for a dog with thinner, lighter hair. Thicker and darker hair could go shorter on the torso, but there the #4-blade-minimum recommendation would be important to consider. Avoid shaving dogs down, but if it becomes medically necessary to do so, make sure the dog wears clothing outside or stays out of the sun until the coat regains a length to protect the skin on its own. ✂️

Resources:

1. Immunophenotypic and ultrastructural evidence of the langerhans cell origin of the canine cutaneous histiocytoma. https://pubmed.ncbi.nlm.nih.gov/8984828/ 
2. Sunlight-skin cancer association in the dog: a report of three cases. https://pubmed.ncbi.nlm.nih.gov/7334163/
3. Langerhans cells: an update. https://pubmed.ncbi.nlm.nih.gov/25482693/
4. Decrease of e-cadherin expression in canine cutaneous histiocytoma appears to be related to its spontaneous regression. https://ar.iiarjournals.org/content/29/7/2713 
5. Animal model: solar dermatosis (keratosis) and solar dermatosis with squamous cell carcinoma. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2042228/