Under normal circumstances, puppies will undergo a hair change at the age of 3 or 4 months, which may last until the age of 8 months.
Since then, when the pet dog has grown up, it will undergo normal physiological hair change in spring and autumn with the change of seasonal climate every year. Note that these are normal physiological changes. You only need to do a good job in daily maintenance and feeding. You don't need to take your dog to see a doctor.
