The plant-based active ingredients in the ONA PRO Gel control odor safely, and without using nose-burning cover-up smells! This standalone smell stopper has almost no scent of its own; all it leaves behind is fresh air. Even when used in extremely odorous conditions, ONA Pro Gel removes almost all traces of unpleasant smells. Gel lasts about four weeks, depending on airflow around the Gel and size of treated area.