Hydrophobic substances are substances that repel or cannot dissolve in water. Hydrophobic literally means having a fear of water (hydro-water, phobia-fear). Hydrophobic substances lack polar groups, or are nonpolar, and therefore are insoluble in water. Lipids are an example of a hydrophobic substance. Oils tend to be hydrophobic substances. The oils that make up the nail polish repel water. If you can see it, there is a droplet of water on top of the painted nail that is repelling the water.