Kojic acid soap is a popular skin lightening soap that contains kojic acid as its main active ingredient. Kojic acid is a natural compound that is derived from fungi and it has been found to be effective in lightening the skin. It works by inhibiting the production of melanin, which is the pigment that gives the skin its color. 

There are many different brands of skin whitening soap on the market, but not all of them are created equal. It is important to choose a high quality soap that contains a high concentration of kojic acid in order to get the best results.

When using kojic acid soap, it is important to follow the directions carefully. Usually, the soap is used once or twice per day. It is important to avoid using the soap on broken or irritated skin.

Some people may experience some skin irritation when using kojic acid soap, but this is typically mild and will go away with continued use. If you experience any severe skin irritation, stop using the soap and consult a dermatologist.

Kojic acid soap can be an effective skin lightening solution for those who are looking for a safe and natural way to lighten their skin. It is important to choose a high quality soap and to use it as directed in order to avoid any skin irritation.