Is there black cotton in sanitary napkins?

The term "sanitary cotton" is a colloquial designation for sanitary napkins in some regions, primarily due to their cotton-like softness. Currently, most absorbent materials used in sanitary napkins are made of cellulose pulp. Cellulose pulp is neither cotton nor contains cotton; it is a wood pulp derived from coniferous trees such as pine, spruce, and fir. It is produced by processing the stems of these natural plants through high-temperature cooking, washing, and purification. Cellulose pulp inherently possesses hydrophilicity, enabling rapid liquid absorption, and has been widely used globally for decades in absorbent hygiene products like sanitary napkins. Since sanitary napkins come into direct contact with human skin, cellulose pulp must meet stringent hygiene standards and cleanliness requirements. During production, cellulose pulp must control microbial growth while preventing contamination by foreign substances. The GB/T 21331—2021 standard "Cellulose Pulp" specifies rigorous requirements for its physicochemical properties, appearance quality, testing methods, inspection rules, and transportation/storage conditions. Microbial indicators are strictly governed by the GB 15979 standard "Hygienic Requirements for Disposable Hygiene Products."

"Blackheart cotton" typically refers to low-quality fiber materials produced by a small number of unscrupulous merchants who recycle discarded clothing, household textiles, or defective products from manufacturing processes. Relevant national standards such as GB 15979 "Hygienic Requirements for Disposable Sanitary Products" stipulate that recycled raw materials should not be used in sanitary pad production, and all materials must be non-toxic and harmless. Legitimate manufacturers do not employ "blackheart cotton" in their production processes, as the term "vulcanized fiber pulp" listed in ingredient tables is entirely distinct from "blackheart cotton." Vulcanized fiber pulp, a naturally sourced absorbent material with excellent performance, is safe when tested according to standards. Claims like "vulcanized fiber pulp causes cancer" or "vulcanized fiber pulp is toxic" lack scientific basis. Some consumers observe shadows in the absorbent layer when exposing sanitary pads to strong light, mistakenly interpreting this as evidence of "blackheart cotton" usage—a practice that is scientifically unfounded. These so-called shadows actually result from uneven distribution of absorbent materials.

Is it unsafe if the villus pulp in sanitary napkins appears yellow under light?

Some netizens have reported that when observing sanitary napkins through lighting, the inner villous pulp appears light yellow, whereas tearing the napkin reveals a white substance. What is the reason for this phenomenon?

It is widely recognized that when light strikes an object's surface, the material selectively absorbs wavelengths. Unabsorbed light is reflected or transmitted to the human eye, creating the colors we perceive. Tests on villous pulp reveal that under D65 lighting (a spectrum approximating natural daylight), the material absorbs blue and violet light more intensely than yellow or orange light—this is a normal physical characteristic of natural wood fibers. However, the absorption rate difference is minimal, making subtle color variations nearly imperceptible to the human eye under normal conditions. When observing light through sanitary napkins, the thicker material layer filters light through multiple layers. The highly absorbent blue and violet light is almost entirely absorbed, while the less absorbent yellow and orange light passes through. This explains why the yellow tint becomes more noticeable when viewing the napkin.

In fact, we can conduct a simple comparative experiment: place a regular sanitary pad and a piece of medical sterile cotton, both made of natural fibers and commonly used in laboratories, under natural light. Both will appear white; however, when observing the light through them, it becomes evident that both exhibit a distinct pale yellow hue.