Hello, Thanks for your query. Some mouthwashes can even cause staining. This is due to a chemical called chlorhexidine gluconate — an antiseptic designed to reduce bacteria and remove plaque, both of which can lead to bad breath. However, when regularly exposed to the teeth it can cause brown patches on the enamel because of a chemical reaction. Some ingredients in toothpaste, such as the foaming agent sodium lauryl sulphate, can interact with the fluoride in mouthwash, and deactivate it Some ingredients in toothpaste, such as the foaming agent sodium lauryl sulphate, can interact with the fluoride in mouthwash, and deactivate it Chlorohexidine can produce tooth staining within about ten days of usage because it reacts with food additives which may be left on the teeth, particularly tannins, found in Coca-Cola, tea, coffee and red wine. I do hope that you have found something helpful and I will be glad to answer any further query. Take care