Canine Recurrent Flank Alopecia (CRFA), also known as seasonal flank alopecia or idiopathic cyclic flank alopecia, is a dermatosis characterized by non-inflammatory hair loss, primarily on the flanks. It is considered a cosmetic issue with no impact on the animal's overall health.

A marked breed predisposition, particularly in Boxers, strongly suggests an underlying genetic component. The condition typically affects dogs aged 3 to 6 years, with no distinction regarding sex or reproductive status. Its seasonality is a characteristic feature, with alopecia often occurring during months with shorter daylight hours. This phenomenon is observed in both hemispheres, pointing to the role of photoperiod as a significant trigger. However, some cases may be sporadic or become permanent.

The exact etiology remains unknown. Systemic endocrine causes have been ruled out. The most robust hypothesis involves the photoperiod, with a potential role for melatonin (production of which varies with day length) and prolactin. Insufficient melatonin production or altered follicular sensitivity in genetically predisposed individuals could be implicated. Genetic studies support a complex polygenic basis, involving disturbances in skin homeostasis that render hair follicles sensitive to seasonal variations. Functionally, it is considered a hair cycle arrest.

Diagnosis is based on clinical signs (non-inflammatory, non-pruritic, bilateral flank alopecia, often with hyperpigmentation) and the exclusion of other causes, such as endocrinopathies. Histopathology of skin biopsies is crucial, typically revealing infundibular hyperkeratosis, atrophic follicles (sometimes described with a "witch's foot" appearance), and a predominance of follicles in the resting phase, although these lesions are not strictly pathognomonic for CRFA.

The vital prognosis is excellent. The condition's evolution varies: it can manifest as cyclic episodes, a single episode, or permanent alopecia. Spontaneous regrowth is common, though the new coat may differ in quality. Given its benign and often self-resolving nature, therapeutic abstention ("benign neglect") is frequently the preferred approach.