what is a demodex
1 Demodex is a mite that lives in small numbers in the skin of healthy dogs and cats without causing a problem. 2  Unhealthy dogs and cats, especially those with immune problems, Cushing's Disease, or on steroid medications can develop severe demodex infection.umans have their own form of demodex mite. The demodex mite is not rareâit is found in small numbers in the skin of most dogs and cats because the mites on their mothers normally travel to young pets shortly after birth.