Hi.. Welcome to HEALTHCARE MAGIC.. I have gone through your query and can understand your concerns.. As per your complain you have a recent history of starting intake of Hyluronic acid and experiencing sore throat, phlegm formation in throat and nasal passages causing nasal congestion.. Well, it does not seems to be due to side effect of Hyluronic acid rather it seems to be due to upper respiratory tract infection, also known as Common Cold and the symptoms of sore throat, nasal congestion and runny nose are all due to cold. The infection will however resolve once the virus will complete its cycle in human body.. As of now you can start with supportive treatment to relieve the symptoms like: 1. Gargle with a warm saline solution that is by mixing 1 teaspoon salt in a glass of water and warm it to make a luke warm solution.. 2. Take a combination of decongestant like Phenylephrine, mucolytic like Ambroxol and anti allergic levocetrizine and another combination of Acetaminophen and Ibuprofen.. 3. Do steam inhalations.. 4. Avoid spicy and chilled foods.. 5. Sip on warm water throughout the day.. Hopefully the symptoms will resolve within a week and if it worsen consult a General Physician and get evaluated.. Hope this information helps.. Thanks and regards. Dr.Honey Nandwani Arora.