If people complain of an unpleasant aftertaste in their mouth, they usually describe it as bitter or metallic. Although this is much rarer, it also happens that a patient experiences a soap aftertaste in their mouth, and this without any contact with soap or any other cosmetic product. In most cases this is a completely trivial problem, but it is also possible that the taste of soap in the mouth is caused by a very serious illness, such as a stroke.