What to Know about Kojic Acid Soap
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Medically reviewed by Brendan Camp, MD
Kojic acid soap is a skin care product used to lighten dark spots on the skin, known as hyperpigmentation. Kojic acid is made from fungi or fermented rice wine.
When used on the skin, kojic acid helps prevent your skin from forming tyrosinase, which is an enzyme that helps create skin pigment (melanin). As a result, using kojic acid soap may help fade dark spots on your skin from acne scars or sun damage. Kojic acid soap is considered safe for your skin, but it may cause some side effects like irritation or sensitivity.
Why Is Kojic Acid Soap Used?
Kojic acid is a skin-lightening ingredient dermatologists recommend for reducing dark spots (hyperpigmentation) and uneven skin tone. When added to soaps and cleansers, kojic acid soap is typically applied to the face or hands and washed off. Over time, using kojic acid soap may help fade sun damage, acne scars, and other hyperpigmentation.
Kojic acid has a controversial history as an ingredient in skin-bleaching products. Skin bleaching is a damaging practice that sets unrealistic and harmful beauty standards for people with darker skin tones. Some kojic acid soaps are still marketed for skin bleaching or “skin whitening” purposes. However, kojic acid does not bleach skin, and dermatologists recommend kojic acid for treating hyperpigmentation on darker skin tones.
Possible Benefits of Kojic Acid Soap
Anecdotally, many people claim kojic acid soap helps fade dark spots. However, there isn’t enough research to prove kojic acid soap works like other kojic acid treatments. Research on the benefits of kojic acid focuses on serums and other topical skincare products, not soap. Still, the lightening and antioxidant effects of kojic acid may also apply to using kojic acid soap.
Dermatologists often use topical kojic acid to treat dark spots of skin called hyperpigmentation. Kojic acid can help treat hyperpigmentation because it is a tyrosinase inhibitor. This means kojic acid blocks your skin’s tyrosinase production and reduces melanin skin pigment. Dark spots are areas with more melanin in those skin cells.
Kojic acid is also an antioxidant, meaning it can help fight harmful compounds called free radicals caused by sun exposure. Free radicals can contribute to the formation of dark spots on the skin.
As a result, kojic acid can help treat hyperpigmentation caused by acne blemishes, sun damage, or melasma. Melasma typically presents as dark patches of skin on the face and often occurs in people with darker skin tones or during pregnancy. Research has found kojic acid is an effective ingredient for fading melasma and other dark spots.
Some research found using just 1% kojic acid reduced participants’ melasma by 58%. However, kojic acid treatments were often more successful in treating pigmentation when combined with other skin-brightening ingredients like hydroquinone or glycolic acid. More research is needed to understand the effectiveness of kojic acid soap.
Risks and Precautions
Using kojic acid soap is not considered dangerous if you use a quality product with a low concentration of kojic acid. Research suggests kojic acid is safer when used in concentrations of 2% or less. However, kojic acid may not be safe for everyone and can cause side effects like:
Sun sensitivity: By reducing UV-protective melanin in your skin, kojic acid makes you more sensitive to the sun, which can increase your risk of sun damage.
Skin irritation: Kojic acid can dry and irritate some people’s skin, especially if you already have sensitive skin.
Allergies: Some people experience allergic reactions to kojic acid, resulting in an itchy and dry skin rash called contact dermatitis.
Before using kojic acid soap, taking the following precautions can help you reduce unwanted side effects:
Try a patch test. Before using kojic acid soap, apply a small amount to the inside of your wrist to see if you have any skin reactions to the soap.
Always wear SPF. Since kojic acid can make your skin more sun sensitive, it's important to protect your skin from damage by applying SPF every day.
Never use on irritated or open skin. Applying kojic acid soap to already sensitive skin can further irritate the area.
Where to Buy Kojic Acid Soap
You can buy kojic acid soap from most stores and retailers that sell skin care products. Major online retailers, health food stores, drug stores, supermarkets, and beauty product retailers often sell kojic acid soap in the beauty or skincare aisles. It's important to buy from a reputable manufacturer when purchasing kojic acid soap.
The U.S. Food and Drug Administration does not approve kojic acid as a drug. Instead, kojic acid products are considered cosmetics—products applied to the body to cleanse or alter appearance. This means the FDA doesn’t have to confirm kojic acid soap is safe before it hits shelves. It’s up to the manufacturer to make sure their product is safe and works as advertised.
The Consumer Product Safety Commission (CPSC)—which regulates soap—also does not regulate kojic acid soap. Even with the word “soap” in its name, kojic acid soap is considered a cosmetic because it is intended to treat the skin, not just clean it.
How to Use Kojic Acid Soap
Add kojic acid soap to your existing skincare routine as a cleanser or spot treatment. You can use kojic acid soap daily on areas with hyperpigmentation, like the hands and face, or you can use it as a spot treatment, only applying the soap on individual dark spots.
Since kojic acid can be irritating and drying, you may find your skin tolerates kojic acid soap better as a spot treatment. Kojic acid also makes skin sensitive to the sun, so it’s often better to use it at night.
Kojic acid soap can take months to show results, and it often takes up to three months for kojic acid products to work. Because kojic acid soap can irritate and dry skin with persistent use, some people use kojic acid soap for a few months and then take a break to help avoid irritation. Some people may also use kojic acid soap every other day to help avoid irritation.
To Apply Kojic Acid Soap as a Cleanser:
Wet the area you want to cleanse with lukewarm water.
Lather your kojic acid soap with water and gently use your fingertips to apply the soap to your skin.
Leave the kojic acid soap on your skin for 1-2 minutes.
Gently rinse the soap off with lukewarm water and pat your skin dry with a towel.
Follow-up with a moisturizer.
Apply sunscreen with an SPF of at least 30 (if you are cleansing during the day).
To Apply Kojic Acid Soap as a Spot Treatment:
After washing your face with a mild cleanser, wet a clean cotton swab or your finger to rub a small amount of kojic acid soap off the bar.
Rub the swab of soap onto areas of hyperpigmentation.
Leave the kojic acid soap treatment on your skin for a few minutes.
Gently rinse off any spots with kojic acid soap using lukewarm water, and pat dry with a towel.
Follow up with a moisturizer on the areas you treated or the entire face if you’re doing your skincare routine.
Make sure you apply sunscreen with at least SPF 30 (if you are treating during the day).
A Quick Review
Kojic acid soap is used to lighten dark spots on the skin caused by hyperpigmentation from acne, melasma, or sun damage. Research shows kojic acid treatments, such as topical serums, can help fade hyperpigmentation.
While there is no strong evidence that kojic acid soap is as effective as the dermatological treatments, it may still help lighten dark spots since it contains the active ingredient kojic acid.
Before trying kojic acid soap, patch test the product on your wrist. Kojic acid can cause irritation and sun sensitivity. You can also use a daily moisturizer and sunscreen to protect your skin.
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