Sarna is the Spanish word for mange, a skin disease caused by microscopic mites that burrow into or live on a dog’s skin. It’s one of the most common and recognizable skin conditions in dogs, producing intense itching, hair loss, and crusty sores that can spread across the body if left untreated. There are two main types, each caused by a different mite, and they behave very differently.
Two Types of Sarna
The two primary forms are sarcoptic mange and demodectic mange. Understanding which type your dog has matters because the cause, severity, and contagiousness are quite different.
Sarcoptic mange (also called canine scabies) is caused by Sarcoptes scabiei mites. These parasites burrow into the outer layer of skin, where they lay eggs and trigger an intense allergic reaction. This is the type most people picture when they hear “sarna.” It spreads easily between dogs through direct contact or shared bedding, and it can even temporarily affect humans.
Demodectic mange (demodicosis) is caused by Demodex mites that naturally live on nearly every dog’s skin in small numbers. In healthy dogs, these mites cause no problems at all. But when a dog’s immune system is weakened or immature, the mite population can explode and cause patchy hair loss and skin inflammation. Demodectic mange is not contagious between adult dogs and is most common in puppies or dogs with compromised immune systems.
What Sarna Looks Like
With sarcoptic mange, the first sign is usually sudden, intense itching. Dogs scratch, bite, and rub themselves relentlessly, and the itching is often severe enough to disrupt sleep and eating. The skin erupts with small, solid bumps, and because the dog damages these bumps through constant scratching, thick, crusted sores develop. The areas hit first are typically the ear margins, elbows, ankles, abdomen, and chest.
If untreated, the sores spread across the entire body. Dogs with long-term, recurring mange develop oily dandruff, severe skin thickening with deep wrinkles, crust buildup, and oozing sores. In severe cases, dogs may lose their appetite, lose weight, and become visibly depressed.
Demodectic mange looks different. It often starts as small patches of hair loss, usually on the face or front legs, without the same frantic itching. Localized demodicosis (just a few patches) is common in puppies and often resolves on its own. Generalized demodicosis, where hair loss and inflammation spread across large areas of the body, is more serious and requires treatment.
Can Sarna Spread to Humans?
Sarcoptic mange can spread to people, though the outcome is usually less severe than what the dog experiences. In humans, it’s sometimes called “pseudoscabies” because the dog-specific mites generally can’t reproduce successfully on human skin. You may develop itchy red bumps on your arms, waist, or other areas that had contact with an infested dog, but the condition is typically self-limiting.
That said, the picture isn’t quite as simple as “it goes away on its own.” Experimental infections have shown that dog-origin mites can survive on human skin for at least 96 hours, and in some cases they’ve hatched eggs and continued developing. Several case reports describe symptoms persisting for weeks. If you’re handling a dog with sarcoptic mange, wearing gloves and washing your hands and clothing afterward is a sensible precaution.
How Sarna Is Diagnosed
Diagnosing mange starts with a physical exam, but confirming the specific mite usually requires a skin scraping. Your vet will use a blade to gently scrape the surface of affected skin, then examine the sample under a microscope looking for mites or their eggs.
The challenge is that skin scrapings don’t always catch the culprit. Mite numbers can be low, especially in early stages of the disease, making them easy to miss. Even in more advanced cases, scraping thickened, crusted skin doesn’t always yield a mite. PCR testing on skin scrapings offers better detection accuracy than microscopy alone, and many veterinary labs now combine both methods to reduce false negatives. In some cases, a vet may diagnose sarcoptic mange based on symptoms and response to treatment rather than waiting for definitive lab confirmation.
Treatment Options
Mange treatment has changed significantly in recent years. The older approach involved repeated lime sulfur dips, which are effective against Sarcoptes and Demodex mites but come with notable downsides: the solution has a strong sulfur smell, can stain light-colored fur, and may irritate skin if mixed too concentrated. Lime sulfur is still used in some situations, but it’s largely been replaced by easier options.
Today, the most common treatments are oral chewable medications in a class of drugs originally developed for flea and tick prevention. Several FDA-approved products in this category are available for dogs, including well-known brands like Bravecto, NexGard, Simparica, and Credelio. These medications work by attacking the mites’ nervous system and are given as a simple chewable tablet, making treatment far more convenient than repeated medicated baths.
One older treatment, ivermectin, is still occasionally used at higher-than-label doses for mange. This requires caution because certain breeds carry a genetic mutation (called MDR1) that makes them unable to safely process the drug. Around 70% of Collies carry this mutation, along with roughly 50% of Australian Shepherds and long-haired Whippets, 30% of McNabs and Silken Windhounds, and 15% of Shetland Sheepdogs. German Shepherds, Old English Sheepdogs, and mixed-breed dogs can also be affected. If your dog belongs to a herding breed or herding-breed mix, genetic testing can determine whether ivermectin is safe. The newer chewable medications have largely reduced the need for ivermectin in mange treatment.
Recovery and Hair Regrowth
Most dogs show significant improvement within the first few weeks of treatment. In studies of generalized demodectic mange treated with fluralaner (the active ingredient in Bravecto), mite counts dropped by 99.8% within 28 days and reached zero by day 56. By days 56 to 84 after starting treatment, the majority of dogs had regrown over 90% of their coat compared to their pre-treatment state.
Sarcoptic mange typically responds even faster, with itching beginning to decrease within the first week or two. Full resolution of skin lesions and complete hair regrowth usually takes one to two months, though severely affected dogs with thickened, damaged skin may take longer. Your vet will likely want to recheck skin scrapings to confirm the mites are gone before stopping treatment.
Preventing Reinfection
For sarcoptic mange, treating the dog alone isn’t enough. The mites can survive off the host for a limited time, so you’ll want to wash all bedding, blankets, and fabric the dog has been in contact with in hot water. If you have multiple dogs, all of them should be treated even if only one is showing symptoms, since the mites spread easily and other dogs in the household may be carrying them without visible signs yet.
Demodectic mange doesn’t require the same environmental cleanup since it’s not contagious between adult dogs. Prevention here is more about supporting your dog’s immune health. Puppies with localized demodicosis often outgrow it as their immune systems mature. For adult dogs with generalized demodicosis, your vet may look for an underlying cause of immune suppression.