How can you determine that protein coagulation is occurring?

When protein coagulation occurs, it involves a physical change in the structure of proteins, typically resulting in a solidification or thickening effect. One clear indicator of this process is the visual transformation that resembles a light frost. This appearance occurs when proteins denature and aggregate, leading to a texture that can be compared to a fine frost covering a surface.

The other options provide various sensory observations, but they do not specifically indicate protein coagulation. Changes in smell, color, or temperature may occur in other contexts but are not definitive signs of protein coagulation like the visual cue of frost-like appearance. In esthetics, understanding these signs can help professionals better gauge when to adjust treatment protocols based on the chemical and physical changes happening in the skin or during procedures involving products that contain proteins.