Commonly used in aesthetic medicine in the form of injections to reduce wrinkles, hyaluronic acid (HA) is a hydrophilic biomolecule capable of capturing and retaining up to a thousand times its weight in water. Naturally present in the body, mainly in the dermis, it ensures the skin's deep hydration. In cosmetics, it is also found in many products for its remarkable anti-wrinkle and plumping properties. But is it safe to use or are there any possible hyaluronic acid allergic reactions or irritations we should know about?