Patch Test Results

A patch test is designed to prove that a product does not irritate the skin.

The product being tested is applied to the skin and remains there for 24 hours. Redness and swelling at the site of the application is observed by an expert to determine irritation levels.

We conducted a patch test with 30 people. According to a dermatologist, the irritation response to our product was 0.0, which indicates a low irritation level.

*Please note that some people may experience irritation regardless of these test results.

*This test was conducted by SOUKEN Co., Ltd.

Making Pure Konjac Products

At Yamamoto Farm, we make products using only konjac, without using any preservatives, antibacterial agents, or petroleum-derived ingredients.
As you can see below, there are no preservatives, antibacterial agents, or petroleum-derived ingredients detected in our konjac products.

No Preservatives or Antibacterial Agents

5-Chloro-2-methyl-4-isothiazolin-3-one is an antimicrobial agent called Methylchloroisothiazolinone, and 2-methyl-4-isothiazolin-3-one is an antimicrobial agent called Methylisothiazolinone. Paroxybenzoic acid is a common preservative called a paraben.

The fact that testing verifies the absence of these ingredients from our products indicates that our konjac sponges do not contain any antibacterial or preservative agents.

No Plastic Ingredients

Phthalic acid is used as a plasticizer to soften materials. Bisphenol A (BPA) is used as a raw material for plastics. Testing revealed that these ingredients are undetected in our products which means that our konjac sponges do not contain any chemical fibers.


Since konjac sponges are not a cosmetic product, there is no obligation to list all the ingredients. However, we at Yamamoto Farm want our customers to be able to use our sponges with peace of mind, so we list all ingredients on our product packaging.

Some konjac sponges are not made in Japan and may contain antibacterial agents not listed on their packaging. You may even see some of these konjac sponges labeled as "100% natural" or "safe for babies."

Real-World Examples
A study of foreign-made konjac sponges distributed in Japan revealed the presence of methylisothiazolinone among their ingredients.

Methylisothiazolinone is an antibacterial agent that is banned for use in products, such as cosmetics, that remain on the skin. It is only allowed to be used in products that are washed off immediately, such as shampoo and rinses. Antibacterial agents are irritating to babies and people with sensitive skin and, in some cases, may cause serious skin problems.

Comparing the Cleaning Power of Konjac Sponges

Konjac sponges neutralize and decompose slightly acidic stains, cleansing pores through the action of slightly alkaline ingredients that seep out from the sponge. Authentic konjac sponges that have been used for generations in Japan are manufactured using only konjac.


Konjac sponges are popular among those with sensitive skin. To remove dirt without irritating skin, we believe sponges should be slightly alkaline with a pH of 8.0 to 9.0.

We compared the pH values of our konjac sponges to those made abroad and obtained the following results.

Yamamoto Farm pH 8.4

·Mildly weak alkalinity
·Gentle on the skin with excellent cleaning power
·Uses only konjac, a process suitable for sponges

Manufactured Abroad pH 6.7

·Neutral with weak detergency
The existence of a konjac sponge with a neutral pH balance is highly unlikely. Considering its unnatural bright white color, it's likely that this sponge contains additives and antibacterial agents. However, the use of these ingredients is undisclosed.

Manufactured Abroad pH 9.5

This sponge has high cleaning power but is also very hard on the skin. It barely falls into the weak alkaline range, but it can cause irritation for those with sensitive skin.

*Specific product names have been withheld.

Why Konjac Sponges are Good for Your Skin A gentle wash that won't scratch the surface of your skin


The stratum corneum, the outermost layer of your skin, keeps bacteria out and moisture in, ensuring that your skin stays healthy. However, when the skin is dry, gaps appear in the stratum corneum and moisture easily evaporates, making it easier for external contaminants to enter. With a thickness of only about .02mm, the stratum corneum is easily damaged, which can lead to skin problems. For example, rubbing too hard can cause inflammation and break the barrier of the stratum corneum, leading to further dryness and irritation, which in turn leads to chronic eczema.

When filled with water, a konjac sponge develops an outer film of water.
When you use it to gently wash your face, the soft 100% natural fibers and the water film will gently remove dirt without damaging the stratum corneum of your skin.