The white film that can occur in your mouth (gums, teeth and inner cheeks) after brushing your teeth with certain toothpaste is likely due to the presence of ingredients in the toothpaste that can create a temporary coating or film in your mouth. This film can be made up of various substances, such as foaming agents, thickening agents, and flavors.

One of the most common culprits is sodium lauryl sulfate (SLS), which is a foaming agent used in many toothpaste brands. SLS can create a layer of foam that covers the surfaces of your teeth and gums, and can also leave a residual film in your mouth after rinsing.

Other ingredients that can contribute to this film include certain flavors and thickening agents, such as carrageenan or xanthan gum. These ingredients can help to create a more pleasant taste or texture in the toothpaste, but they can also leave a temporary coating in your mouth.

While the white film can be a bit unpleasant, it is generally harmless and you can remove it by rinsing and swishing water in your mouth.

If you find that the film persists or causes discomfort, you may want to try using a different brand of toothpaste that does not contain SLS or other ingredients that can create this effect.