Just when the weather turns cool and your pooch should be his plushiest, he starts losing fur over his flanks. What’s up with that?

If the hair loss is symmetrical — that is, equally apparent on both sides of your dog’s body — and doesn’t involve itch or inflammation, it could be seasonal alopecia [al-oh-PĒSH-ah]. If so, hair loss typically occurs between November and April when days are shortest. Light-associated changes in the hormones melatonin and prolactin are thought to be a cause.

Seasonal alopecia most often affects boxers, but you might see it in English bulldogs, Airedale terriers and schnauzers, too. It usually first shows up when dogs are 3 to 6 years old.

If your pooch regrows hair as the days lengthen but the same thing happens next year, keep seasonal alopecia in mind. Your veterinarian can provide additional advice.