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Check for fleas. Check for sarcoptic mange. Check for cheyletiellosis, or walking dandruff. Check for lice. Check for demodectic mange. Check for ringworm. Understand what should not be causing itchiness.
The most common cause of itchy skin is fleas. They are most active in warm, humid weather (35°C or 95°F). You may see the fleas on your dog, or you may just notice your dog biting or scratching their skin. Fleas are very quick and can jump very high, so you will need to be fast to spot them. Fleas are most likely to be found in the armpit and groin area and are dark (almost black) with flat bodies.  Check your dog's ears for signs of scratching, redness, blood, or dirt. See if their belly, groin, or the base of their tail has red bumps. One way to check for fleas is to stand your dog over a white surface, such as paper towels or pieces of paper, then comb their coat. Flea feces will fall out when you comb the dog and it will be more visible on the white paper. Sarcoptic mange (Sarcoptes scabiei) is a parasitic mite infestation. Mites will usually live in areas of the skin that do not have hair such as the ear flaps, elbows or stomach. The dog may have red, scaly skin in these areas. Sarcoptic mange can cause significant skin lesions and distress for the dog because the mite causes severe itching.  Sarcoptic mange is contagious and can be transmitted to people and other dogs very easily. Your veterinarian can diagnose sarcoptic mange by collecting skin scrapings from your dog. This is caused by the Cheyletiella mite that feeds on the top layer of skin. In addition to excessive scratching, the dog may have scaling on the skin, hair loss, dandruff, lesions on their back.  It is sometimes called "walking dandruff" because the mite pushes up scales of skin as it travels, making it appear as though the scales are moving. You might be able to see the mite, which is yellow. Dog lice is different from human lice, so don't worry about infecting each other. Lice survive on either your dog's skin debris or their blood, depending on the species. You should be able to spot adult lice on your dog — they are yellow or tan and about the size of a sesame seed. They can sometimes be mistaken for dandruff, but will not fall off the dog if you shake the hair. Other signs of lice include hair loss (especially around the neck, ears, shoulder, groin, and anus); a rough, dry, or matted coat; small wounds or infections; tapeworms or other parasites that can be spread by lice; and even anemia in severe cases or in small dogs. Demodectic (red mange) is caused by small mites found naturally on most dogs. These mites do not generally cause skin problems unless the dog’s immune system is compromised. Demodex is most commonly seen in puppies, because their immune systems are still developing. This mange is most noticeable around the eyes and mouth. It can be diagnosed by your veterinarian collecting skin scrapings from your dog.  Demodectic mange is not very contagious and people cannot contract it. It is generally passed on to nursing puppies by the mother.  A predisposition for this skin problem may be inherited. It is not uncommon for the puppies to have Demodex if their parents also had Demodex at some point in their lives. Ringworm is not actually a worm; rather, it is a fungus. It causes itching, small circular scabbing (about a centimeter in diameter), and hair loss (alopecia) in one or more areas on your pet. This typically starts on the face or paws. Ringworm is contagious and easily transmittable to humans (a zoonotic disease) and other pets. Your veterinarian will be able to diagnose ringworm and advise you on the treatment protocol, which will require a fungicide.  Some pets with minor infections can be treated topically, whereas other animals will need oral anti-fungal medication. Treatment of ringworm will also include disinfecting your home. It may take months to control. Your dog may have a condition that resembles a parasite or other condition that might mislead you in determining the cause of his itchiness. Alopecia and Cushing’s disease are two possible conditions.  Alopecia, or hair loss, can be brought on by low thyroid (hypothyroid) conditions and is not typically itchy. Low-thyroid dogs tend to have more skin issues than normal-thyroid dogs.  Dogs with Cushing’s disease will drink a lot of water and want to eat all the time. You may notice that the dog’s fur is thinner and has less undercoat. The dog’s belly may even be nearly bald and the skin looks thinner too.