What Is Kojic Acid Soap and How Can It Help Your Skin?

Kojic acid is made from different fungi species and is a byproduct of fermented rice. Kojic acid soap is used in skincare routines as a skin-lightening soap. However, what are kojic acid's potential benefits, and how may it help your skin? Here, we shed light on these questions and on the side effects of using this soap for hyperpigmentation.

What is kojic acid?

Kojic acid is produced from over 58 fungi, including Aspergillus and Penicillium species. Kojic acid can also be produced through rice fermentation — it is the byproduct of the fermentation process of making a traditional Japanese rice wine known as sake.

Kojic acid is useful in food and cosmetic industries because of its potential antioxidant properties and its ability to preserve or change the color of substances. Therefore, it is commonly used for skincare products, e.g., hyperpigmentation products.

Kojic acid in skincare

Kojic acid is usually found in skincare products in different forms:

• Serums
• Powders
• Creams and lotions
• Soaps

What is kojic acid soap?

Kojic acid is known to block an enzyme known as tyrosinase — the enzyme that plays a role in the production of melanin (i.e., skin pigment). Because of this property, it is popularly used in skincare, especially as a soap.

While kojic acid is promoted for its gentle exfoliating properties and potential to lighten darker skin areas, it is best to consult with a dermatologist before using new skincare products, especially for more serious skin issues like acne scarring. A dermatologist can help you choose the right products for your specific skin concerns.

Potential benefits of kojic acid soap for the skin

According to the American Academy of Dermatology Association, kojic acid is recommended for managing uneven skin tone and hyperpigmentation because of its different potential benefits. Although some promising research outcomes exist on kojic acid on the skin, its effectiveness can vary based on the concentration and formulation of the product being used. Therefore, for more serious skin issues like acne scarring, it is ideal to consult with a dermatologist to help you choose the right results for your specific skin concern.

Currently, most studies on the benefits of kojic acid are in animals, but there are not many studies on humans. Also, it should be noted that kojic acid is not a solution on its own. It should be used as a skincare routine to address skin concerns. Proper hygiene and other methods and products a dermatologist prescribes are needed for adequate skin issue management.

May brighten and lighten skin

Kojic acid is one of the most reviewed skin-lightening agents. It has been shown to reduce the appearance of dark spots and hyperpigmentation.

A 2023 study on 12 people with post-acne skin investigated the application of a 3% kojic acid solution using kojic acid powder and saline. The solution was left on the skin for two, three, or four minutes and was repeated 4–6 times at two-week intervals. The results showed that kojic acid increased skin brightness in 75% of the individuals.

Despite this promising result, the number of individuals in the study is small; therefore, more large-scale studies are needed to properly assess the potential effectiveness of kojic acid on a broader population.

As mentioned above, kojic acid may block the enzyme that plays a role in melanin production (i.e., skin pigment). Because of this property, it could be used to reduce the overproduction of melanin, resulting in a more even skin tone over time and making it an option for discoloration management.

May help with acne scars

Because of its skin brightening and potential wound-healing properties, kojic acid soap may help manage acne scars. Kojic acid may contribute to reducing the appearance of acne scars by lightening them and potentially supporting their healing.

Its anti-inflammatory properties may also soften uneven skin texture often left by acne scars. However, those with severe acne scaring should still consult a dermatologist before incorporating this acid into the skincare routine, as it may not be universally suitable for all skin types or conditions.

Anti-aging properties

Kojic acid is known to have antioxidant properties. Therefore, it could help protect the skin from oxidative stress caused by free radicals. These can potentially break down collagen and elastin in the skin, contributing to the wrinkle and fine line appearance. Kojic acid has also been shown to potentially contribute to the reduction of age spots.

However, despite these benefits, remember that kojic acid is not the sole solution to aging-related skin concerns. It should be used as part of a comprehensive skincare routine.

How to use kojic acid soap

There is no specific guideline on how to use kojic acid soap. However, below is general guidance on using it effectively to avoid potential irritation and increase the chance of seeing some results.

1. Start with a patch test. Do a patch test on a small area of skin (for example, the back of your ear or your inner arm) to check for any potential side effects.
2. Add water. Wet your skin so that it can better absorb the kojic soap. Depending on your skin concerns, you may use the soap for your face or body.
3. Use the soap. Gently massage the soap to form a lather on your skin. Ensure to avoid your eye area and sensitive areas like cuts or sores. If it’s your first time using the soap, you could leave the lather on your skin for a few seconds (20–30 seconds). However, if you are more experienced, you could work the leave-on time to a few minutes (1–2 minutes). You may experience dryness if you leave the soap on your skin for too long.
4. Thoroughly rinse. Use water to rinse off all the soap, with no residue remaining on your skin.
5. Moisturize. Follow up with a moisturizer to restore hydration to your skin.
6. Apply sunscreen. Use a broad-spectrum, water-resistant sunscreen (SPF 30 or higher) to protect yourself from sun damage because kojic acid may make your skin more sensitive to the sun. Ensure to apply it to all skin that will be exposed to the sun.

You may start using kojic acid soap once or twice a week. Then, if your skin tolerates it and if you don’t experience any side effects like irritation, you could work your way up to a few times a week or daily.

How long does it take for kojic acid soap to work?

According to the American Academy of Dermatology Association, discoloration/dark spots may fade away within six to 12 months.

Although there are different published studies on the effectiveness of kojic acid, there is no published study on the effectiveness of kojic acid in a soap formulation. The topical application of a kojic acid ointment showed some initial changes after eight days.

Typically, you may start to see results of kojic acid use after four to eight weeks. This depends on your skin type, skin concern, and frequency of use. Using it consistently and following any specific instructions on the product label may lead to more optimal long-term results.

Precautions and side effects

Whatever skin condition you may have, bear in mind that kojic acid is still just that — an acid. Therefore, it is essential to consult with a dermatologist about using acid on your skin before including it in your skincare routine and to ensure it is suitable for your specific skin type and skin concern.

Some reported side effects of kojic acid are skin irritation and redness. Other potential side effects include allergic reactions, dryness and flakiness, and increased sensitivity to the sun. Apart from using a broad spectrum, water-resistant sunscreen, there are other steps you can take to prevent or manage some of these side effects:

1. Use a skin-type appropriate moisturizer. After using kojic acid, it is important to use a hydrating moisturizer that is specific to your skin type. This is because kojic acid could dry your skin.
2. Have short leave-on times. If you are new to using kojic acid, start with short leave-on times (maybe 5–15 seconds) to check your skin’s tolerance. After a while of consistent use, then you may slowly build up the leave-on time. This could prevent irritation.
3. Patch-test. Always patch-test the soap on a small area of skin, avoiding sensitive areas.
4. Start slow. Start with a frequency of once a week, and then slowly build this up to maybe twice a week. If you do not experience any side effects, you may increase this to three times a week.
5. Stop. If you experience any allergic reactions like swelling or severe redness and/or rashes, stop using kojic acid and consult with your dermatologist if the symptoms do not resolve.

Who should avoid kojic acid soap?

So, is kojic acid safe? Although kojic has potential skin benefits like skin brightening and skin tone evening, it may not be suitable for every skin type.

If you have sensitive skin or existing skin conditions like eczema, rosacea, and dermatitis, you should avoid using it because it may aggravate these conditions. Also, pregnant or breastfeeding individuals may want to avoid it as there is no published study of its use in this population of individuals. Always speak with a dermatologist before using kojic acid.

People with broken skin or open sores may want to avoid using kojic acid soap as it may cause irritation and discomfort.

Final word

Kojic acid is claimed to have different potential benefits: from being a soap for hyperpigmentation to being useful in anti-aging skincare. Take some time to ensure it is suitable for your specific skin type and skin concerns because it may not be useful for those with sensitive skin or with certain existing skin conditions.