Black spots on a dog's hair follicles can be the result of infection, scabbing, parasites or heredity or acquired diseases. Knowing the cause of a particular black spot is useful in determining the course of action to treat and prevent these black spots when necessary.
Folliculitis is a disorder of the hair follicles, and is sometimes a result of another infection such as scabies, seborrhea or hormone-related disease. Aggressive grooming stresses the follicles and also can cause folliculitis. In milder cases, a dog's skin may have small, inflamed areas filled with pus. As infection progresses, these areas can rupture and form scabs, which may have a blackish appearance as the associated blood dries. A form of folliculitis called schnauzer comedo syndrome can result in numerous black spots along the middle of a dog's back.
Acanthosis nigricans is a condition that causes blackening of the skin, including the hair follicles. This condition can affect many breeds and ages, and can be genetic or develop later in life. If it's genetic, it usually occurs before the dog is a year old. Whether genetic or acquired, Acanthosis nigricans causes the skin to become darker and thicker and produce discharge in many cases. Other signs can include patchy hair loss, itchiness or inflammation of the skin.
Mites and Fleas
Mites can affect dogs' skin and hair follicles. Ear mites, for example, cause a dog's ear canals, including the hair follicles, to become irritated, crusted and scabby. This results in a wax-like discharge that resembles coffee grinds. Whether a dog has ear mites or another mite, these nasty parasites can cause scabbing, which can appear black. Fleas also can leave black debris, flea excrement, on a dog's fur and skin.
Although sometimes big and engorged with blood, ticks start out small, and many are black. A tick feasting on a dog for a while can grow 20 to 50 times its original size. In the meantime, ticks can seem like nothing more than a black spot on a dog's skin or hair follicle. Smaller species and nymphs -- immature ticks -- are devious because they are as small as the period at the end of a sentence.
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