The possible reasons for the swelling in hamsters may include the following:
Bacterial Infection: Hamsters may develop swelling due to unhygienic surroundings or bacterial infections. The treatment method is to clean the hamster's utensils, keep the environment dry and hygienic, and wipe the swollen area with normal saline.

Fungal Infection: Fungal infections can also cause swelling in hamsters. The treatment method is to shave the hair around the affected area, disinfect it with hydrogen peroxide, iodine tincture, or alcohol, and then spray medications that can treat both fungi and bacteria.
Allergic Reaction: Certain bedding materials or foods may cause allergies in hamsters, leading to swelling. The treatment method is to find and remove the allergen, clean and disinfect the cage and its accessories, and replace the food with a lighter diet and the bedding with a new type.
Parasitic Infection: Parasites such as mites and ticks can also cause swelling in hamsters. The treatment method is to disinfect the area and use appropriate antiparasitic medications.
Preventive Measures and Nursing Suggestions:
Keep the Environment Clean and Dry: Regularly clean the hamster's cage and utensils, and avoid a damp environment to prevent the growth of bacteria and fungi.
Adjust the Diet: Avoid feeding too many foods that can cause excessive internal heat, such as melon seeds and peanuts. Keep the diet light and supplement with a variety of vitamins and trace elements.
Use Medications: Under the guidance of a doctor, use appropriate medications for disinfection and treatment to ensure that the medications will not cause secondary harm to the hamster.
Wear an Elizabethan Collar: Prevent the hamster from licking the affected area, which may lead to an aggravation of the infection.
Through the above measures, the swelling problem of hamsters can be effectively alleviated and treated, ensuring their healthy recovery.