Polyacrylamide is a gel created by the process of electrophoresis, a technique used in biochemistry and molecular biology to separate macromolecules. It is a cross-linked polymer of acrylamide and because it is an acoustic coupling medium, it can be used for focused ultrasound therapy. While acrylamide is highly toxic, the ingredients used to make ultrasound gel are non-toxic and safe to use by trained medical professionals.
Propylene Glycol is an organic, double oil compound frequently used for cosmetic purpose. It is used as a humescent in ultrasound gel, which results in a retention of moisture. In combination with the other ingredients, propylene glycol does not usually irritate the skin, though it is toxic if ingested.
Glycerine is a polyol compound often used in pharmaceutics and for making items such as soap. It is neutral, sweet-tasting and colourless. It is an ideal ingredient for the use in gels because it is an effective solvent and absorbs water from the air.
Phenoxyethanol is a glycol ether. It is often used in skin and other dermatological products. It is water-soluble and breaks down into phenol and acetaldehyde. In 2008, the U.S. Food and Drug Administration warned that phenoxyethanol is potentially toxic and can damage the nervous system.
Though they differ by brand, most ultrasound gels contain a blue colourant, such as FD&C Blue No. 1. Colorants are synthetic dyes usually made from petroleum. These dyes are commonly found in food, cosmetics and pharmaceuticals.