Kojic acid soap is a type of skin lightening soap that contains kojic acid as its active ingredient. Kojic acid is a natural compound derived from a fungus that can inhibit the production of melanin, the pigment that gives skin its color. As a result, kojic acid soap is often used to lighten dark spots, age spots, and other forms of hyperpigmentation on the skin.
Kojic acid soap is also believed to have antioxidant properties that can help protect the skin from damage caused by free radicals. Some people also use it as an anti-aging treatment to reduce the appearance of fine lines and wrinkles.