Importance: Nonanimal cross-linked hyaluronic acid (HA) dermal fillers are among the most versatile tools in minimal invasive esthetic medicine. Filler injections aim to volumize, provide contour, and reduce wrinkles and skinfolds. In the hand of the experienced user, HA fillers have an excellent safety profile. Nevertheless, adverse events have been reported related to poor injection techniques, infection, and immune reactions. Observations: In this review, the focus is on filler impurities. Impurities can originate from the fermentation process, crosslinking, packaging, and contamination. Impurities consist of particular and nonparticular matter. We discuss possible risks for the patient to be treated with HA fillers. Conclusions and Relevance: Impurities of dermal fillers bear a potential risk for patients, such as delayed autoimmune and inflammatory reactions, biofilm formation, and exposure to leachable Endocrine Disrupting Chemicals. Amount and quality of impurities can be considered as one of the quality parameters of commercially fillers. Considering patient safety, filler impurities should be further reduced.