A safety concern has been raised on the basis of several studies regarding the effect of toothpaste SDS on aphthous ulcers (more specifically, mouth ulcers or "canker sores"), commonly referred to as canker or white sores. According to the NHS, SLS is a cause for concern for mouth ulcers. As Lippert notes, of 2013, "very few... marketed toothpastes contain a surfactant other than SLS [SDS]," and leading manufacturers continue to formulate their produce with SDS.