Causes of Dermatitis
The causes of canine skin problems – or “dermatitis,” which means inflammation of the skin - can be elusive and vary widely. It is helpful to have a general idea of the anatomy of the skin, to understand what happens when it becomes irritated and inflamed. The skin is the largest organ in mammals. Most of us don’t think of the skin as an “organ,” but it indeed is a living, complex, connected network of cells and tissues that continuously interacts with the inner and outside world. The most external layer of skin is called the “epidermis.” The epidermis is a superficial, sometimes scaly layer of the outermost skin that does not have its own blood supply. The layer of skin directly below the epidermis is the “dermis.” It does have a blood supply and contains the hair follicles, sweat glands, sebaceous glands and toe nails. Sweat glands are only found in a dog’s foot pads, which is why dogs only sweat through their feet. Hair follicles are indentations in the dermis that give rise to long primary guard hairs which make up a dog’s topcoat, shorter accessory hairs that make up the undercoat and special hairs of the whiskers and eyelashes. Sebaceous glands, which are also part of the dermis, are connected to the hair follicles. They secrete “sebum,” which is a greasy substance that lubricates the dog’s skin and coat. Sebum is what makes a dog’s coat shiny. It also helps protect the coat from water.
Anything that irritates a dog’s skin can cause dermatitis. Often, this starts an itch-scratch-itch cycle, although sometimes dermatitis is only noticeable by patchy hair loss. Some causes of canine dermatitis include:
- Contact with irritating animal, vegetable or chemical substances
- Exposure to extreme heat, cold or humidity
- Mechanical irritation
- Self-trauma (biting, chewing, rubbing)
- Hot spots; acute moist dermatitis
- External parasite infestation (fleas; flies; ticks; mites; lice; maggots)
- Skin allergies/hypersensitivity/atopy
- Mange (sarcoptic; demodectic; other)
- Food allergies
- Immune-mediated or auto-immune disorders
- Infectious disease (bacterial; fungal; viral)
- Hormonal diseases (Cushing’s Disease; Addison’s Disease; hypothyroidism; hypoestrogenism; hyperestrogenism; others)
- Interdigital cysts (between the toes)
- Skin abscesses
- Puppy acne
- Skin fold pyoderma
- Tumors or masses (cysts; hematomas; lipomas; adenomas; melanomas; papillomas; others)
Allergic reactions to external parasites (fleas, flies, ticks, mites, lice, mosquitoes), and allergies to certain types of foods, grasses, detergents, plants or other environmental allergens, are among the leading causes of dermatitis in dogs. Dermatitis can also accompany systemic disease. Genetic factors may also be involved. Sometimes, the underlying cause of dermatitis is never discovered.
Allergic reactions to external parasites can be prevented by successful use of topical and environmental anti-parasitic medications. All companion dogs should be fed a high-quality, well-balanced diet, which can help prevent hypersensitivity reactions to poor food ingredients. Medicated shampoos that contain naturally soothing ingredients can also help prevent itchiness and moisturize the skin.