Hair loss can occur in many different situations, including, but not limited to poor nutrition, autoimmune disease, fungal infections, allergies and/or parasites. The most important thing to note is the skin condition - is the skin inflamed, crusty, "normal," or full of scabs? If your pet is experiencing hair loss of any kind, it is best to have it checked out to find out the underlying cause.
Baldness, or alopecia, isn't "normal" in animals (with exception of certain breeds, like the Chinese Crested (hairless dog).
So anytime a bald spot is noticed, your veterinarian should have a look.
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 "psychogenic 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).
Please note: this article has been provided for informational purposes only. If your pet is showing any signs of illness, please consult a veterinarian as quickly as possible.