Makers of hyaluronic acid fillers like Juvederm admit to what they call hypersensitivity reactions at the rate of 1:5000 to 1:8000 injections. They are not really classified as allergic reactions. I have seen one patient with such a reaction in a patient injected by her gynecologist. The reaction went on for months with swelling and itching. I would not get this type of injection close to your wedding day.
Hyaluronic acid products are natural and not from animals, so an allergic reaction is extremely rare. There are isolated reports of all kinds of reactions from fillers, but these are also extremely unusual. However, I have a policy of NOT doing anything new to a bride close to her wedding just in case you don't like what it does. Another nice thing with Juvederm and other Hyaluronic Acid products is that if you don't like the result, it can be dissolved.
Juvederm and Restyane are Hyaluronic acids and are very safe substances. Unlike collagen injections,which are no longer used, there is no skin test required because the risk of allergy is negligible. That being said, there is always a chance, even if it is extremely small, of an allergy to anything. Most importantly is to find a board certified dermatologist with a great deal of experience in cosmetic dermatology for the best results.
We have hyaluronic acid in our bodies, where it works as a natural lubricant in our joints and skin. So you should not have an allergic reaction to it. Some people will get swelling in certain areas where juvederm is not the best choice for a filler, such as in the lower lid or tear trough. Because it swells after it goes into the skin, this is not an allergic reaction, but an expected result. Restylane or belotero are better for these areas. If you are worried, try some a few months before your wedding. If you don't like the result you can reverse it. As for the reports of dizziness and mental disturbances, those people probably had those issues before getting any injections.
Hyaluronic acid fillers are very safe, and have a very low risk of complication. Hyaluronic acid has very little reactivity with the immune system. If you are concerned about reactivity you can always ask the surgeon to place a small amount in a "test spot" in an inconspicious place on the face, typically behind the ear. Although, test spots are not necessary for routine hyaluronic acid filler injections. Good Luck
An allergy to any of the class of hyaluronic acid fillers is unlikely and would be unusual. The Juvederm and Restylane family have the longest history with the least risks . There are many fillers out there being manufactured that do not have such a great track record and are usually not offered in US physician offices. The HA family also is reversible which is a nice safety net in case a patient does not like their results or has complications. Complications are rare in trained hands and the reversibility of the product is just a bonus . See a board certified dermatologist for your first injection . Ask them about their experience and always express your concerns prior to treatment.