Was alarming at first because it hissed when I first opened it and had an odd smell. A brief google confirmed that this was a common experience with other concentrated vitamin C serums and may be normal. Apprecirate the really dark glass bottle (phone flashlight was barely visible through the bottle) and the separate dropper, as the vitamin c is required to be protected from light.

Only been using it for a few days, but it seems to be more sticky than other generic vitamin Cs I've used, perhaps from the hyaluronic acid component.