What are these little white dots under my lip after Juvederm XC injection? (Photos)

These may be fordyce spots. You may also have swelling which can be typical. Icing and cold compresses may give improvement. I would wait a full 2 weeks before judging the results. If it is after the two week wait, you can have the filler reversed with hyaluronidase.
I hope this helps!

Thank you for sharing your question and photographs. Though some degree of firm bumps from filler is expected with a lip augmentation what I think you are referencing in your picture are fordyce spots present along your lip border.  These are normal findings in patients and do not require treatment.  Hope this helps.

There can be some swelling and/or lumps after lip injections which can last 1-2 weeks. You can apply firm pressure between two fingers on the lips for a few days, for 5 mins a time, in order to help decrease swelling and even out the lumps. If you're unhappy with your final results you can have it reversed with hyaluronidase and try a different technique next time. Best, Dr. Emer

These are most likely the result of the filler placed superficial . May be from the injection technique . Lumps usually go away after a couple weeks. You can massage them. It can also be reversed with hyuronidase . Give it some time to see if you are happy after the swelling goes down and it settles. Dr. Banta 

Filler material rarely appears as dots although that is possible. Massage of lip may help. Injecting hyaluronidase would dissolve then if they persist. I would also be concerned about herpes simplex of the lip, especially in a patient prone to cold sores.I short course of antiviral medicine acyclovir pills and ointment would be indicated.