Hydrogels

What Are Hydrogels?

Hydrogels are hydrophilic gel systems consisting mainly of water or an aqueous-alcoholic mixture, together with a gelling agent. They typically contain around 85–95% water.

The gelling agent is generally an organic polymer, such as polyacrylic acid (Carbopol), sodium carboxymethylcellulose, or nonionic cellulose ethers.

Properties of Hydrogels

Hydrogels provide a light, easily spreadable texture and produce a cooling effect after application, mainly due to evaporation of the solvent. They can also provide an immediate moisturising or hydrating sensation.

Because the high water content makes hydrogels susceptible to microbial contamination, they require an appropriate preservation system.

Formulation Considerations

As water evaporates from a hydrogel applied to the skin, the remaining polymer can leave a sticky or film-forming sensation. The choice of thickener and other formulation aids therefore has an important influence on the final sensory properties.

For longer-lasting application, humectants such as glycerol (glycerin) may be incorporated to help reduce the drying effect associated with solvent evaporation. Appropriate selection and testing of the gelling agent, humectants and other adjuvants are essential for achieving the desired texture and skin feel.

References

Handbook of Cosmetic Science and Technology – André O. Barel, Marc Paye, Howard I. Maibach.