By April Garbuz, Wilton High School

Standing in the drug store, we see two types of mascara: water-soluble and water proof. Despite the fancy names and colorful packaging, the true difference between lash lengtheners is whether the ingredients are dissolved in water or oil.

The molecules in water-soluble, or hydrophilic (water loving), mascara are water, glyceryl stearate, ammonium acrylates copolymer, polyvinyl alcohol, and alcohol. Since water is the primary molecule, we know that the next items are water-soluble, meaning they are easily dissolved in water. Polyvinyl alcohol has many purposes, one of which is to act as a good adhesive, binding the liquid to the lash. Additionally, alcohol is a useful ingredient as it is soluble in both polar substances (water) and non-polar (oil) substances.

Waterproof, or hydrophobic (incapable of dissolving in water), mascara contains petroleum distillate, polyethylene, carnauba wax, pentaerythrityl hydrogenated rosinate, and tall oil glycerides. The word wax, oil, or fat indicates that we are dealing with hydrophobic molecules. These all are organic compounds called hydrocarbons that must be dissolved in an oily substance (petroleum distillate) in order to be in a liquid/gel form that can be easily applied to lashes.

When you jump in the pool, waterproof mascara does not run because the only way to dissolve the bonds between the mascara and your lashes is to use oil based make-up remover or solvent that can break the bonds.

More on the science of beauty: How Lip Plumpers Work
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April Garbuz is a TalkingScience summer intern and a junior at Wilton High School. She loves science, debating, acting, and swimming. Ultimately, she'd like to be a research scientist.