Can Juvederm make an old hypertrophic scar worse?

This is difficult to answer without pictures, but it is unlikely that Juvederm is causing this. Hypertrophic scars can be improved with a combination of vascular lasers like yellow laser, Aerolase, microneedling/prp, skin lightening, peels, and skin care. Sun protection is essential. I recommend getting a formal evaluation with a cosmetic dermatologist. Silagen gel should be used twice daily with jan marini bioshield.  Best, Dr. Emer

Thank you for sharing your question.  Unfortunately without feeling your tissues or seeing a full series of images it is difficult to offer definite advice.  HA fillers like Juvederm do not "stimulate" your natural collagen formation like Bellafill or Sculptra so it is unlikely that they caused worsening of the scars but what is more common is that they made the scar more prominent from stretching the tissues.  I would see an ASPS board certified plastic surgeon in consultation, they can offer you the best source of advice. 

Because JUVÉDERM is an HA filler, it works by adding volume directly rather than stimulating collagen production so an injection should not have any impact on an existing scar. There are several treatments available that could help improve the appearance of a hypertrophic scar. Check with a board-certified cosmetic surgeon to develop a customized plan that will help you meet your goals.