- Health Library
- PetMD U
The most common response a pet caretaker makes when they see their dog scratching and biting at itself is “I think he’s got fleas”. And sometimes this guess is correct. Dark, copper colored and wingless, and about the size of the head of a pin, fleas are big enough that they can be seen scurrying along the skin surface trying to hide within the sheltering forest of fur. (Read more about fleas and what to do about them here)
There are a number of highly effective and safe flea preventatives. Fleas are ubiquitous, but an understanding of their life cycle, where they hide in the dog’s environment, and utilizing modern pharmacology breakthroughs, no dog needs to be "driven crazy" with itching and scratching, hair loss, infections, scabs and other skin problems as a result of flea infestation.
Repeated exposure to fleas can trigger a hypersensitivity (an abnormal, excessive reaction) to the bite of even a single flea. Every veterinarian has been fooled into making a diagnosis of “allergy”, not even suspecting fleas, simply because no fleas were discovered at the time of the physical exam. This is a classic example of a Parasitic Dermatitis (flea bites) triggering a complicated Allergic Dermatitis (due to the flea saliva).
Interestingly, the all-too-common parasite called the tick rarely triggers itching and scratching or allergic reactions, but on occasion will leave an ulcerative lesion that is notoriously slow to heal.
Chiggers, deer flies, and gnats (sometimes called No-See-Ums) can be considered nuisances and generally do not create remarkable systemic skin problems. Local treatment with first aid ointments generally is successful.
Cheyletiella mites look like tiny spiders under a magnifying glass and are often called "Walking Dandruff" because upon close inspection it seems like little flakes of dry skin are actually moving about. Partly because they live on the surface of the skin, these tiny critters can be eliminated easily by using any common flea shampoo. And here’s a creepy thought … Cheyletiella mites can be transmitted to humans where they create, just like on the dog, alopecia (hair loss) with a dry, flaky, slightly pruritic skin surface.
Sarcoptic mites are nasty critters! Also called scabies or red mange, they create very intense itching and scratching, alopecia, and inflamed skin with multiple small scabs often present. Sarcoptic mite infestation, more than any other entity, is frequently misdiagnosed as Allergic Dermatitis by even very competent and experienced veterinarians. There is a good discussion of Scabies here).
Many veterinary dermatology specialists will not accept an uncontrolled "Allergic Dermatitis" referral case unless the referring veterinarian has first ruled out Sarcoptic mites by actually treating the dog for scabies. Do as many skin scrapings as you like, you’re not going to find these little rascals because, unlike most skin parasites, these burrow right down into the skin. (Even ticks simply hold on to the surface of the skin while they feed; ticks do not burrow into the skin.)
Unfortunately, many dogs are treated with cortisone for a supposed allergic dermatitis when in fact these Sarcoptic mites are the cause of the pruritic, inflamed skin... the unnecessary cortisone eventually worsens the situation.
Sarcoptic mites happen to have preferences … certain types reproduce and thrive on dogs, but they do not thrive on other species such as humans. Nevertheless, Sarcoptic mites from dogs can infest humans so if your dog has signs of scabies and you are itching and have little scabs, make sure you see your dermatologist (MD, not DVM)!
Mention your concern about scabies mites. If your physician makes a diagnosis of scabies, your next call should be to the veterinarian to make an appointment to discuss the possibility of Sarcoptic mites in your dog (the one that’s been getting all those cortisone shots for "allergy").
Then there are Demodex mites -- also called "mange." These little rascals do live and reproduce just under the skin surface in the tiny hair follicles and oil glands of the skin.
Unlike Sarcoptic mites, Demodex mites can be seen on a skin scraping viewed under the microscope. They look like tiny cigars with stubby legs stuck to the front half of their body.
Demodex is most commonly seen in young dogs. In adult dogs, Demodex cases seem to be associated with individuals that are stressed from disease, poor nutrition, immune disorders or a harsh environment.
There is evidence that many cases of Demodex have a genetically transmitted immune protein deficit underlying its manifestation; the dog’s breeder should be informed of any cases of Demodex mites.
If the dog is otherwise healthy, there are effective treatment protocols for Demodex. On the “itch scale”, Demodex causes very little itching and scratching. On the “baldness scale” Demodex creates mottled and patchy alopecia.
Bacterial, fungal and yeast organisms are notoriously obnoxious pathogens causing coat and skin problems in dogs (and cats). Fungal organisms are called dermatophytes. One type, called Microsporum canis, causes non-pruritic, circular patches of hair loss, often called ringworm. Transmissible to other dogs (and occasionally some strains of fungi can be transmitted to humans) your veterinarian can diagnose and treat skin fungal infections in the office.
Yeasts, most notably a common contaminant of inflamed and environmentally stressed skin called Malassezia pachydermatitis, can irritate an already diseased skin surface. Especially notorious for creating long term, low-grade external otitis, Malassezia does cause itching and scratching and inflammation.
Yeast infections typically create greasy, odorous and pruritic signs in affected dogs. The skin is stressed by the waste products of the organisms and responds by releasing histamine -- which triggers further inflammation, itching and scratching and cell damage.
If a yeast infection is diagnosed, there’s generally something else going on such as hypothyroidism, chronic administration of cortisone medication or dietary fatty acid deficiency.
Bacterial dermatitis rarely occurs spontaneously. Normal healthy skin has tremendous numbers of a variety of bacteria present all the time. If something upsets that balance, such as antibiotics eliminating one or two types, the remaining types have a free-for-all! Anything that damages the normal, healthy, intact skin will hamper the skin’s defense mechanisms. Any Environmental Dermatitis, such as contact with grass, plastic, an abrasion or moisture, can adversely affect the skin’s defensive barriers and opportunistic bacteria then have their way. Parasitic damage to the skin will allow invasion by bacteria and trigger the body’s healing defense mechanisms.
A common skin problem in dogs, Infectious Dermatitis often is so irritating that dogs will lick continuously at the lesion and undo any healing that has taken place. A moist, sticky, inflamed skin lesion along with hair loss is characteristic of bacterial dermatitis. These can spread rapidly and even be transposed to other areas of the skin through biting, licking, and scratching of previously uninfected areas.
The treatment for Infectious Dermatitis often includes clipping the hair from the area to allow the air to assist drying. The application of gentle topical medication is helpful as is the administration of oral antibiotics to fight the organisms that are deeply invading the skin.
Yes, cortisone may assist in alleviating the stinging or itchy sensation, but may also suppress normal healing processes. Whenever an infection is present, the decision to use cortisone needs to be very carefully evaluated. A better choice may be antihistamines orally.