Underlying every successful cosmetic product is the ability to deliver consistent quality every time it’s purchased by a consumer. Understanding how moisture affects quality can help achieve the quality customers demand.
The power of powder
Many cosmetics products are compacted, tinted powders. The compaction and flow properties of these substances are controlled by water activity (aw). During the manufacturing process, knowing the critical water activity of a powdered product can assure equipment isn’t loaded full of a powder that won’t move. When the blended powder is ready to be formed into the packaging, water activity influences how tightly the powder is compacted. Any variation in a product’s water activity will affect its physical properties.
Water activity controls bacterial growth in cosmetics
Water activity, and not moisture content, determines what bacteria can grow in a product. Cosmetics tainted with bacteria can cause irritations and infections on the skin and in eyes. Even if products comply with GMP requirements, customers may not be as careful. Formulating a product with a water activity below 0.87aw will guarantee that even if it picks up trace amounts of bacteria during use, the bacteria won’t grow.
Water activity: a better way to measure moisture
Many cosmetics manufacturers monitor the moisture content of their products, but for a particular product, water activity and moisture are linked; if one goes up, so does the other. This means that water activity is actually a better way to measure moisture. Why?
- Water activity meters are much more sensitive to changes in moisture than most moisture content meters. This is because on dry cosmetic products, a tiny change in moisture creates a large change in water activity. When compared with AOAC approved moisture methods like oven drying, water activity gives you about 10 times more precision.
- Karl Fischer titrations are renowned for their precision, but lack speed, ease of use, and affordability. A water activity test gives you the precision of Karl Fischer without the costly reagents, glassware, and specialized training.