What can I do to prevent the puffy face after under eye fillers?

Firstly, it's important to note that some degree of swelling is normal after any type of filler injection. However, if you're experiencing excessive swelling or puffiness in the cheek area after under eye fillers, there are a few things you can do to help reduce it:
Apply ice packs: Applying ice packs to the treated area can help to reduce swelling and inflammation. Be sure to wrap the ice pack in a cloth or towel to prevent direct contact with the skin.
Avoid strenuous exercise: Avoid any strenuous exercise or activities that may cause you to sweat excessively for at least 24 hours after the treatment.
Sleep with your head elevated: Sleeping with your head elevated can help to reduce fluid accumulation and prevent puffiness.
Massage the area: Gently massaging the treated area can help to distribute the filler evenly and reduce any lumps or bumps that may be contributing to the puffiness.
Stay hydrated: Drinking plenty of water can help to flush out any excess fluid and reduce puffiness.
If these methods do not work, you may want to consider talking to your injector about dissolving the filler. Dissolving the filler with an enzyme called hyaluronidase can be an effective way to address overfilled or uneven areas.
Overall, it's important to work with a trained and experienced injector who can help to minimize the risk of complications and provide guidance on post-treatment care. Be sure to follow any specific instructions given by your injector and don't hesitate to reach out if you have any concerns.

One syringe of fillers under the eyes should not create puffiness throughout the cheeks. You can try watching sodium intake to see if there is an improvement. Could it be related to allergies? If you are confident it is related to the filler and cannot find resolution you can elect to have the product dissolved.