Why does hydrogen peroxide fizz and form white foam when applied, and is this normal?

Fizzing and white foam are a normal chemical reaction. When hydrogen peroxide comes into contact with skin and dirt, active oxygen is released. It is this oxygen that forms the bubbles, which mechanically help lift dirt particles off the surface.

How strong the reaction is depends on how dirty the treated surface is and how active the enzymes on the skin are (catalase and peroxidase, which are present in all living tissue). On clean skin the reaction will be weaker; on a dirty area it will be more noticeable.

It is important to understand that vigorous fizzing does not mean the product is “working deeper” or more effectively: the solution acts only on the surface. Prolonged or too frequent contact with the same area of skin can dry it out slightly, so after application let the skin dry naturally and apply a moisturiser if needed.

If the reaction seems excessively intense or is accompanied by a burning sensation that does not go away, rinse the solution off with water and do not apply it to that area again.