Injectable hyaluronic acid do not carry any risk as long as they are administered by a qualified professional. Being a natural substance, it is very safe and does not usually present side effects.
The percentage of people who have suffered from some allergy or reaction ranges from 3% to 5%. In case of any side effects, they usually disappear after a few days.
Some side effects are sensitivity, bruising, or lumps in the applied areas. Discomfort, irritation, hardness, and redness of the skin may present as well.