Why does my dog have dandruff?

The ASPCA's cold-weather advice describes the pattern exactly: repeatedly coming in from the cold to the dry heat of a home can cause itchy, flaking skin. Its fixes are simple. Keep the house humidified, towel your dog dry as soon as it comes in, and bathe as little as possible during cold spells, because washing too often strips the coat's essential oils and makes dry, flaky skin more likely. A Cape Ann winter ticks every box: wind off the water, wet walks and a furnace running for months.

Salt water adds to it. From October 1 the Gloucester beaches reopen to dogs, at the time of writing, and a dog that comes home from Good Harbor or Wingaersheek with salt drying in its coat has had its skin dried out twice. A fresh-water rinse and a towel after a salty walk is kinder to the skin than a full shampoo every time. If the flakes last into spring, or arrive with any of the other changes on this page, ask your vet to look further.

Seborrhea is the medical name for skin that produces too much oil and scale. VCA describes a dry form and an oily form, says most affected dogs have a mix of both, and lists cocker spaniels, West Highland white terriers and basset hounds among the breeds with an inherited version. The skin may be red and crusty, with a brown, waxy buildup and a smell. Merck advises following your vet on the right medicated shampoo and never using one made for people without the vet's consent.

Walking dandruff is something else entirely: Cheyletiella, a mite that VCA calls uncommon but highly contagious to dogs, cats, rabbits and people. Its main sign is scaling along the back and upper body, sometimes with itching, and the moving flakes that give it its nickname. VCA notes that people are affected only briefly, that every pet in the household should be treated at the same time, and that bedding and surfaces need thorough cleaning. If flakes seem to move, call your vet before the next groom.