Flank Alopecia (Seasonal Alopecia) in Dogs

Flank Alopecia (Seasonal Alopecia) in Dogs

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Overview of Flank Alopecia (Seasonal Alopecia) in Dogs

Flank alopecia is a condition characterized by hair loss over the trunk of the dog’s body that is probably genetic. Flank alopecia is also known as canine recurrent flank alopecia (CRFA), canine idiopathic cyclic flank alopecia, cyclic flank alopecia, cyclic follicular dysplasia and seasonal flank alopecia.

Flank alopecia manifests as hair loss followed by regrowth that reoccurs over an animal’s lifetime. Most dogs are affected between November and April during shorter durations of sunlight however it can occur anytime of year in some dogs. Dogs can have the disease reoccur yearly. Hair regrowth make take several months with a range of 1 month to 14 months.

Some experts believe that seasonal changes in melatonin and prolactin secretion at the hair follicles and follicular hormone receptors may affect hair growth.

Affected breeds include boxers. It is thought that boxers may account for over half of all cases of flank alopecia in dogs. Other dogs that may be affected include English bulldog, Airedale terrier, and schnauzers (all sizes). Age of onset is generally 3 to 6 years and can affect both males and females.

What to Look For

Signs of Flank Alopecia (Seasonal Alopecia) in Dogs may include: 

  • Bilaterally symmetrical recurrent hair loss followed by hair regrowth
  • There is no skin inflammation
  • Hair loss occurs over the flanks on both sides and back (from ribs to lower back)
  • Some dogs can also have hair loss at the base of the ears, base of the tail and perineum
  • Well demarcated borders
  • Areas of hair loss often have increased pigmentation
  • Occurs most often between November and March
  • Hair regrowth can take 3 to 8 months
  • This disease is not itchy

Diagnosis of Flank Alopecia in Dogs

Flank alopecia can often be diagnosed by breed and symptoms alone, however skin biopsy is strongly recommended for definitive diagnosis. Dogs over 2 years of age are often tested for hypothyroidism to ensure this is not a cause of the dog’s clinical signs.

Treatment of Flank Alopecia in Dogs

Flank alopecia does not require treatment because the condition is cosmetic.

Some clinical evidence exists that melatonin may stimulate hair growth in some dogs. Melatonin is often dosed at 3 to 6 mg per dog every 8 to 12 hours.

Dogs less than 20 pounds generally are prescribed 3 mg of melatonin every 12 hours and dogs over 20 pounds 6 mg every 12 hours. Up to 75% of dogs may benefit from melatonin therapy. Some dogs can start melatonin 1 to 2 months before expected hair loss to minimize hair loss or immediately upon hair loss to short the duration of the hair loss episode. Injectable implants of melatonin can be used but their safety has not been confirmed.


Dogs with flank alopecia can live a normal life. The impact is cosmetic in nature. Dogs with follicular alopecia are prone to sunburns.

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