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Why do many dogs grow thicker coats in autumn?

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A Labradoodle dog runs energetically through grass with a stick in its mouth, ears flopping and tail raised. — dog A Labradoodle is a cross between a Labrador Retriever and a Poodle, a mix intended to incorporate the Poodle's intelligence and low-shedding coat with a Lab's energy and determination.

Many dogs grow thicker coats in autumn as a natural response to seasonal changes, primarily driven by the amount of available daylight, a phenomenon known as photoperiodism. As days become shorter in the fall, this environmental cue triggers the dog's body to grow a longer and thicker coat to prepare for colder temperatures.1

This process is part of the dog's natural molting cycle, which allows mammals to adjust their insulation requirements based on the season. While daylight is the primary driver for this change, temperature also influences the density of the coat; dogs living in colder climates typically grow thicker hair and more protective undercoats than those in warmer regions. This seasonal adaptation is essential for thermoregulation, helping the animal maintain its body temperature by providing an effective barrier against the environment.213