According to MedicineNet, there is a huge range of causes for hair loss in dogs. The most common reasons include allergies, parasite infestation, stress or illness.
WebMD describes the process of dogs shedding fur, which is worse during spring and summer, as a normal process for most breeds, as they shed their excess or old fur. Hair loss in dogs, or canine alopecia, presents in a variety of ways and is a cause for concern, according to MedicineNet, which also states that hair loss appears as bald spots, in patches, generalized across large areas of the body or in one or two localized spots.
According to MedicineNet, allergies are a very common cause of hair loss in dogs. Dogs can potentially suffer from a range of allergies, including food allergies, environmental allergies, such as pollen and grass or allergies to parasites, which results in generalized itching, scratching, and hair loss.
Pets4Homes states that another common cause of hair loss in dogs is stress or anxiety. If a dog has a nervous disposition or is exposed to stress in any form for a long period of time or severe stress for any length of time, it can present as scratching, licking and chewing, resulting in bald patches.
If a dog is losing fur without an obvious cause and has a regular parasite prevention plan, seek veterinary attention as soon as possible.