Talking about SURFACTANTS means talking about high performing soluble products that, by definition, are able to lower the surface tension of the system thanks to their molecular structure:

Hydrophilic Head + Hydrophobic Tail.

In Ceramics, for example, when the surfactant is added to a glaze suspension, the following happens on the surface:

the tail, due to its hydrophobic property, remains outside the water (exposed to the air) while the hydrophilic head, that is soaked, separates the water molecules that are in the top layer, therefore lowering the surface tension.

The reduction of the surface tension of the glaze produces a better application on the tile and thus a better leveling.

Being completely soluble, even if they do not normally produce any particular surface defects such as holes or pinholes (especially due to the low usage rates), surfactants can sometimes be highly foaming and not easily manageable.