Wet wipes, an indispensable part of modern life, are essential for many people to maintain hygiene and convenience. However, with the growing prosperity of the wet wipes market, potential problems have gradually surfaced. Among them, wet wipe contamination is of particular concern.

In 2024, the National Medical Products Administration (NMPA) issued a notice regarding 575 batches of non-compliant wet wipes and the detection of banned ingredients in wet wipes. Among them, 165 batches failed microbial-related non-compliance items such as total bacterial count, total mold and yeast count, and Pseudomonas aeruginosa.

On the 17th, the Shanghai Municipal Food and Drug Administration issued the first 2024 wet wipes quality inspection notice, revealing that 15 batches of wet wipes in Shanghai failed inspection, including those with excessive total bacterial counts. These microorganisms could not only undermine product stability and effectiveness but also pose a threat to consumer health.

This raises the question:

Why are wet wipes so susceptible to microbial contamination?

What factors in wet wipes influence microbial growth?

Key Factors Affecting Microbial Growth in Wet Wipes

Understanding the key factors that influence microbial growth in wet wipes is crucial for ensuring their safety and quality.

We know that microorganisms exist in every corner of our daily lives and in nearly every part of nature. Wet wipes have a long lifecycle, from production and storage to consumption, which can take anywhere from months to years. Many of the ingredients in wet wipes that are naturally beneficial to the skin (such as water, oils, and various skincare nutrients) are also favored by ubiquitous microorganisms and provide them with excellent nutrition, making the wet wipe microenvironment a breeding ground for microbial growth and reproduction.

1. Water

Water is a key ingredient in wet wipes. Many wet wipes contain a certain amount of moisture, which is conducive to microbial growth. Water is also an excellent solvent. Substandard water quality can easily compromise the product's preservative effectiveness and foster microbial growth.

2. Temperature

The production and storage temperature of wet wipes is suitable for the growth and reproduction of most pathogens. 37°C is the optimal growth temperature for most pathogens, while the optimal growth temperature for mesophiles is 20°C-40°C. The optimal growth temperature for most molds and yeasts is 20°C-30°C. Therefore, for routine testing, we typically set the incubator temperature for bacteria at 36±1°C and for molds and yeasts at 28±2°C.

3. pH

The type and number of microorganisms are also related to pH. The optimal pH for surface bacteria is approximately neutral at 6-8, while yeasts and molds thrive in slightly acidic environments. Therefore, the optimal pH for microorganisms closely matches the pH range of the wet wipes themselves.

4. Nutrition

To enhance product efficacy, wet wipes contain a rich supply of nutrients such as protein, fat, various vitamins, and minerals. However, these ingredients can easily encourage the growth and reproduction of microorganisms, leading to the deterioration of the wipes.

Therefore, the liquid in wet wipes plays a crucial role in inhibiting microbial growth and preventing deterioration.

Wet wipe liquids contain quaternary ammonium salts or other antimicrobial ingredients that effectively kill or inhibit bacteria and viruses. Surfactants, meanwhile, remove dust and oil stains from the skin and surfaces.

Wet wipe liquids often also contain humectants and antioxidants such as glycerin, aloe vera extract, chamomile extract, and vitamin E. During use, these moisturize and soothe the skin, while also mitigating irritation to a certain extent.

In short, the liquid in wet wipes is the heart and soul of wet wipes, inhibiting microorganisms and ultimately determining their effectiveness.