Extreme itchiness and the resultant licking, chewing, biting will cause hair loss (traumatic alopecia). This can be seen as blunted stubble in the affected area.
But what about situations where there isn't any itching? When the skin looks normal - not red, inflamed or seemingly bothered? You still need to have it checked out. It could be a hormonal imbalance (i.e. hypothyroidism - more common in dogs), ringworm, or what is commonly known in cats as "pyschogenic alopecia". This is now recognized as an obsessive compulsive behavior wherein the cat, continually "overgrooms" an area, perhaps due to stress.
Another feline baldness condition is something called Eosinophilic Granuloma Complex (ECG), and this is an allergic condition in the skin, often with accompanying scabby areas.
As you can see, there are many conditions that can cause baldness with or without itching in cats and dog. Other conditions not mentioned above include parasites other than fleas (Demodex mites, Notedres mites).