Japanese Spitz dogs have several downsides including heavy shedding due to their thick double coat which requires regular grooming, and they are not hypoallergenic. They can suffer from health issues such as patellar luxation (kneecap dislocation), arthritis, eye problems like cataracts and glaucoma, and other conditions like runny eyes and cancer. Behaviourally, they may experience separation anxiety leading to destructive behaviour if left alone too long, and they tend to be quite vocal, barking frequently which requires training to manage effectively.