Dogs get demodex mites from their mothers, almost always within the first few days of life. The tiny, cigar-shaped mites transfer during nursing as the puppy’s face presses against the mother’s skin. Nearly every dog carries these mites as a normal part of its skin fauna, and most never develop any problems from them. Disease only happens when something allows the mite population to multiply out of control.
Mother-to-Puppy Transfer During Nursing
The primary route of transmission is vertical, from mother to newborn during suckling. As puppies nurse, the mites crawl from the dam’s skin onto the puppy’s muzzle, face, and front legs, then gradually spread to other parts of the body. This transfer happens in the first days of life, and by roughly one week of age, a puppy’s developing immune system is already strong enough to resist colonization by new mites. That narrow window is why virtually every dog ends up carrying demodex mites but only picks them up once.
Because this is such a universal process, demodex mites are considered part of the normal skin ecosystem in dogs. They live inside hair follicles and oil glands, feeding on skin oils and cellular debris. In small numbers, they cause no symptoms at all. Most dogs live their entire lives without ever knowing the mites are there.
Can Dogs Catch Mites From Other Dogs?
Demodectic mange is not considered contagious, and vets generally don’t recommend isolating affected dogs. The classical view has been that after the first week of life, a dog simply won’t accept new mites onto its body. However, this idea has been challenged in recent years. Occasionally, multiple unrelated dogs in the same household develop demodicosis, which is hard to explain if no dog-to-dog transfer is possible.
Current thinking is that mites can transfer between adult dogs, but in a healthy dog, the newcomers simply join the existing mite population at low numbers and never cause skin disease. In rare cases involving severe infection in one dog, the spread of actual disease to another may be possible. Still, the practical takeaway is clear: you don’t need to separate a dog with demodectic mange from your other pets the way you would with sarcoptic mange, which is highly contagious.
Why Mites Multiply: The Immune System Connection
The real question isn’t how dogs get the mites. It’s why the mites sometimes explode in number and cause hair loss, redness, and skin infections. The answer is almost always an immune system that isn’t keeping the population in check.
Research has shown that dogs with demodicosis have a measurable shift in their immune cell balance. Specifically, they have fewer helper T-cells (the ones that coordinate the immune response) and more suppressor T-cells (the ones that dial the response down). The ratio between these two cell types drops significantly in affected dogs, and the imbalance is even more pronounced in dogs with generalized demodicosis compared to those with just a few localized patches. This immune suppression, whether inherited or caused by another illness, is what gives the mites room to proliferate.
Puppies vs. Adults: Different Triggers
Demodicosis in puppies and young dogs (typically under 18 months) is usually tied to an immature immune system that hasn’t fully developed its ability to regulate mite populations. Most cases of juvenile demodicosis resolve on their own or with treatment, and many puppies outgrow the problem as their immune system matures.
Adult-onset demodicosis, appearing in dogs older than about four years, is a different story. When an adult dog that has been healthy suddenly develops demodectic mange, it often signals an underlying condition suppressing the immune system. Research published in The Veterinary Record found significant associations between adult-onset demodicosis and specific diseases: overactive adrenal glands (Cushing’s disease), underactive thyroid (hypothyroidism), and in certain regions, leishmaniosis. Cancer, long-term steroid use, and other immunosuppressive therapies can also trigger mite overgrowth. If your adult dog is diagnosed with demodicosis for the first time, your vet will likely want to investigate what else is going on.
Breeds at Higher Risk
Genetics play a meaningful role. A large VetCompass study from the Royal Veterinary College identified specific breeds with elevated risk. For juvenile-onset demodicosis, seven breeds stood out: English Bulldogs, Staffordshire Bull Terriers, Chinese Shar-Peis, Dogues de Bordeaux, Pugs, French Bulldogs, and Boxers. For adult-onset disease, six breeds showed increased risk: Chinese Shar-Peis, Shih Tzus, West Highland White Terriers, Boxers, and Border Terriers.
The genetic component is thought to involve inherited weaknesses in the T-cell immune response that specifically governs mite control. This is why responsible breeders generally avoid breeding dogs that have had generalized demodicosis, since the immune deficiency can be passed to offspring.
More Than One Type of Mite
At least two species of demodex mites infest dogs. The most common, Demodex canis, lives deep inside hair follicles and causes the classic pattern of patchy hair loss, scaling, and redness. A second species, Demodex injai, is longer-bodied and tends to live in the oil glands of the skin rather than the hair follicles. Dogs with Demodex injai often develop unusually greasy, oily skin (a condition vets call seborrhea oleosa) rather than the typical dry, patchy look of standard demodicosis. Demodex injai is less common but worth knowing about because its symptoms can look quite different and may be misdiagnosed.
Both species are transmitted the same way and managed similarly, but the clinical picture they produce can vary enough that skin scrapings or other diagnostic tests are important for identifying which mite is involved.
What Demodicosis Looks Like
Localized demodicosis usually appears as a few small, round patches of hair loss, most often on the face, around the eyes, or on the front legs. The skin in these patches may look slightly pink or scaly but isn’t usually intensely itchy. Many cases of localized demodicosis in young dogs resolve without treatment over six to eight weeks.
Generalized demodicosis is more serious. It involves widespread hair loss, thickened or inflamed skin, and frequently secondary bacterial infections that cause pustules, crusting, and a strong odor. This form can be intensely uncomfortable for the dog and requires veterinary treatment. The bacterial infections that accompany severe cases are often what cause the most discomfort and can become dangerous if left untreated.