Canine Alopecia Secondary to Human Topical Hormone Replacement Therapy in Six Dogs

This report described six cases of alopecia in dogs, which were linked to accidental transdermal exposure to their owners' topical hormone replacement therapy (THRT). The affected dogs, from three different households, exhibited hair loss on various body parts and signs of feminization, with normal serum thyroxine levels. Skin biopsies revealed consistent histological features, and all dogs had elevated estradiol levels, with some also showing increased progesterone. The average time for symptoms to appear was 5.5 months after THRT began. Notably, discontinuing THRT led to complete resolution of symptoms in all dogs within 5.5 months.