The safety of sanitary napkins depends on more than just pH value

“I don’t even buy Class C clothes, yet the sanitary napkins I use directly against my skin are only Class C standard?”

“No wonder I feel itchy down there as soon as I put on a pad during my period — I finally found the cause!”

Recently, the topic “Sanitary Napkins Class C” has gone viral on social media.

It started when netizens discovered that the current national standard for sanitary napkins (pantyliners) sets the pH value at 4.0–9.0, the same range required for Class C textile products — which are not intended for direct skin contact — under the National General Safety Technical Code for Textile Products.

Many netizens questioned:

The vaginal environment is naturally weakly acidic. Could long-term use of neutral or slightly alkaline sanitary napkins harm women’s bodies?

In response to these questions, multiple gynecological experts told reporters from People’s Daily Health Client that this is a misunderstanding about the relationship between the pH value of sanitary napkins and the pH value inside the vagina.

Experts explained:

“Sanitary napkins only touch the surface of a woman’s skin, at a distance from the actual vaginal canal.

Therefore, it is difficult to say that the pH value of the napkin itself directly affects the vaginal environment.”

Furthermore, for healthy women, the internal vaginal pH is not easily disturbed by external factors such as the pH of sanitary napkins.

Lactobacilli in the vagina convert glycogen into lactic acid, maintaining a normal acidic environment and inhibiting the growth of other pathogens — a mechanism known as the vaginal self-cleaning function.

In addition, a woman’s vaginal pH naturally changes during different physiological stages (such as menstruation, after intercourse, menopause, etc.).

Under normal conditions, the vagina is weakly acidic, with a pH usually ≤ 4.5 (3.8–4.5).

However, during menstruation, menstrual blood has a higher pH than the vaginal environment, causing the internal vaginal pH to rise to around 6.

On November 12, the Market Supervision Administration of Yuxi City, Yunnan Province, also issued Yunnan Consumers Association Comparative Test (II): Sanitary Napkins, stating that “according to national standards and relevant provisions, the pH value of sanitary napkins (including pantyliners) shall be between 4.0 and 9.0. A pH value within this range is considered relatively neutral or close to the natural pH of women’s private parts, thus reducing skin irritation and discomfort.”

In addition, based on testing and analysis of 10 sanitary napkin products from different channels (physical stores and e-commerce platforms) conducted by the Yunnan Consumers Association, the pH values of all 10 samples ranged from 5.7 to 6.2.

“The balance of vaginal microecology is determined by a combination of factors including estrogen levels, local vaginal pH, lactobacillus levels, and the vaginal mucosal immune system. When this balance is disrupted, a series of problems such as inflammation may occur. Therefore, we should not focus only on pH while ignoring the influence of other factors,” experts noted.

“During menstruation, changes in vaginal pH and the open state of the vaginal opening create conditions for pathogen growth. If personal hygiene is neglected at this time, it may also lead to illness.”

“Besides, sanitary napkins are generally only used during menstruation, and individuals have different sensitivities to sanitary napkin materials. For example, intolerance to ‘dry mesh surfaces’ can also cause the feeling of itching as soon as the napkin is applied,” experts added.

Doctors reminded the public that as long as the pH of sanitary napkins does not cause irritation or damage to the skin and mucosa, it is acceptable. “What matters more is that the product is soft, comfortable, breathable, free of pathogenic bacteria, and fully meets hygiene standards.”

In accordance with China’s mandatory standard GB 15979-2002 Hygienic Standard for Disposable Hygienic Products, the microbial requirements for ordinary-grade feminine hygiene products are:

total bacterial count ≤ 200 cfu/g,

total fungal count ≤ 100 cfu/g,

and coliform bacteria and pathogenic pyogenic bacteria shall not be detected.

For healthy women, when purchasing sanitary napkins daily, in addition to pH value, they should pay more attention to the product’s inherent quality and hygiene conditions. Unhygienic sanitary products have been proven to have a clear inducing effect on vaginitis.