In just the same way humans with stressful jobs acquire the “salt and pepper” look at a younger age, dogs who had undergone a harder life were found to have acquired grey hairs earlier than those with a more care-free existence.

Scientists involved in the study, published in the journal Applied Animal Behaviour Science, said they had long suspected stress manifested itself in this way, but that finding evidence for the theory had been challenging.

The research involved visiting dog homes and veterinary clinics across the state of Colorado.

Owners were asked 42 questions about the lifestyle, health, behaviour and appearance of their animals.

This included whether dogs destroyed things when left alone, if they cowered when in groups of people and if they suffered hair loss.

Impulsivity, such as how often a dog jumped up on people, was also measured.