Bald patches or hair loss in dogs are not the same thing as normal shedding. If you notice a sudden irregularity in a dog's hair growth after grooming and it does not grow back as it typically does, or if atypical bald patches appear, this is definitely not shedding. The cause may be simple and easily treated or a symptom of a more serious condition.
Frequent Causes of Baldness
One of the most common causes of hair loss in dogs is allergies. If environmental factors such as airborne irritants or pollen are causing allergies they can result in hair loss or open wounds called hot spots. Dogs, especially larger breeds, can get calluses or thick raised hairless bumps, particularly on joints. Other common baldness causes include pregnancy, advanced age, folliculitis or infected hair follicles. Cushing's disease is another more common cause, which also results in frequent bruising.
Less Common Causes
Some dogs will experience hair loss following clipping or grooming, and this reaction is called post-clipping alopecia and occurs often following surgery especially in breeds such as chows and huskies. Sebaceous adenitis causes circular bald patches and arises from defective sebaceous glands. Sometimes following a ringworm infection, hard bumps and hair loss can occur; this is called kerion. Lice infestations and flea allergies can also lead to hair loss.
Other Causes of Hair Loss
Sometimes nutritional deficiencies cause hair loss in dogs, including B vitamins and copper or protein deficiencies. Hormones can create bald spots or hair loss as well, including with low thyroid function or low-growth hormone. Mange is another significant cause of hair loss and is associated with severe or possibly complete baldness. It is highly contagious and may be spread to humans. It's caused by a parasitic mite and causes inflammation of the skin with extreme itching.
Ensuring a healthy diet, or possibly adding nutritional supplements, will treat nutrition-related hair loss symptoms. Hormone imbalances can be treated with hormone therapy. Calluses can be treated by providing softer bedding and padding. Post-clipping alopecia requires time and patience for the hair to grow back. Infections, parasites or mites and allergies can be treated with medications. Mange treatment varies, but medication will be required.