The reasons why dogs lose hair in patches:

1. Skin diseases: After suffering from skin diseases, dogs will scratch and bite with their claws and teeth due to itching. This results in massive hair loss and hair loss.

2. Food problem: Dogs only eat dog food without taking in other nutrients, which will lead to malnutrition, hair loss, hair loss, and in severe cases, all hair loss. Do not give human food to dogs, as it will cause hair loss and hair loss.

3. Frequent bathing: Do not bathe your dog frequently, as it will destroy the protective layer on the dog's skin, and you must use pet-specific shampoo.

4. Parasites: Reduce contact between dogs and sick dogs when going out to avoid being infected with infectious diseases and parasites. Also give your dog deworming medicine regularly.

5. Endocrine problems: Hypothyroidism or Cushing's disease can also cause dogs to lose hair in patches, and some are symmetrical. At this time, relevant examinations are required, and if there are problems, corresponding treatment is required.

6. Caused by allergies: After the dog drinks the food, it becomes allergic to food, meat, or the environment, the grass or plants it goes to, and hair loss will occur after contact. If the owner cannot make a judgment, it is recommended to go to the animal hospital to see an animal doctor for a comprehensive judgment.