Unless it’s spring and Fido is shedding, it can be disconcerting to see that your dog is losing lots of hair.

In dogs, alopecia usually indicates something’s wrong—whether that means a skin issue or an underlying medical condition. The most common types of hair loss are caused by parasites such as mange and fleas, rather than the metabolic basis that symmetrical hair loss tends to have, according to Dr. Samantha Devine, DVM, a Virginia-based veterinarian and pet expert. “When dogs have symmetrical hair loss, it almost always results from an underlying health issue, usually a hormonal or glandular problem,” Devine says.

What Causes Hair Loss in Dogs?

Mange is a common cause of hair loss in dogs. “One of the most common types of mange is Demodex, which causes hair loss, or alopecia, by living around the hair follicle; the area gets inflamed, and the hair falls out,” says Devine. “Mange caused by Sarcoptes is a little different: this mite causes the pet to itch and the hair falls out.” Symmetrical hair loss, on the other hand, occurs for a variety of reasons. For some dogs, hypothyroidism, or low thyroid levels, triggers hair to fall out, usually on the sides of the body, Devine explains. Cushing's disease can cause a variety of problems in dogs, including hair loss, and it tends to be symmetrical, as well, according to Devine. “Dogs may also develop autoimmune diseases that cause symmetrical alopecia. In some dogs, such as Boxers and Bulldogs, changing of the seasons can trigger seasonal flank alopecia, which can result in symmetrical hair loss,” she adds. A host of other problems can cause hair loss, including allergies and fungal infections such as ringworm. “Fleas are one of the main causes of hair loss in dogs, generally caused by the itching and scratching that dogs do because the saliva of the fleas causes intense itchiness,” says Devine.

Diagnosing Alopecia in Dogs

Alopecia in dogs is diagnosed through a variety of tests. The first step is always an exam—and if there are obvious causes for alopecia, like fleas, this might be all that’s needed for a diagnosis. Routine tests include a skin scrape, where a sample of skin is scraped away to look for mites, and a skin impression, which lets your vet know if your pup has yeast or bacteria in its skin, according to Devine. “Fungal cultures are used to diagnose ringworm, while skin biopsies may be used for diagnosing autoimmune diseases, tumors, and other problems,” Devine says.

Treating Hair Loss

How you treat your dog’s hair loss depends greatly on what caused it in the first place—and this is why it’s important to always talk to your veterinarian, so they can decide what treatment is best. For example, if your dog has fleas or other parasites, flea preventives may be used to kill the parasite. “Antifungal medications are used to treat ringworm and metabolic disorders are usually treated by either supplementing the missing hormone or suppressing an excess of hormones,” says Devine. “Autoimmune diseases are normally treated by using immunosuppressive medications.”