Dandruff occurs when the skin cells flake off, usually due to dry skin. However, if the dandruff on your dog appears to be black in color, it may be a symptom of something else.
Dog dandruff is generally not black. If your dog has what seems to be black dandruff, it may actually be the result of fleas or canine lice.
Flea feces can appear to be black dandruff. It is often described as being waxy or similar in appearance to dirt. In some cases, if the feces gets wet, it will smear and produce a red-like color.
The dandruff might be the nits, or eggs, of canine lice. These nits are cemented to the hair shaft and will not shake loose like dandruff would.
On a dog, fleas and lice can cause a variety of symptoms: skin lesions, itching--which may be mild to severe--and hair loss.
If you see what appears to be black dandruff on your dog, you should have a qualified veterinarian provide a diagnosis.
If your dog's black dandruff proves to be lice, there is no reason to panic. Canine lice is not the same species as those found on humans and cannot be transmitted to humans.