Eyebrow mascaras let you brush and color your brows all at once. They provide you with an easy way to color your brows while giving you a bit of control. Use brow mascaras when: 1.) You want to thicken thin eyebrows. Not everyone needs them, but if you have thin eyebrows, brow mascara can be a lifesaver. 2.)You have messy eyebrow hair. Brow mascara provides a good degree of control and helps you keep your stray brow hairs in place. 3.) You want to match on contrast your brow and hair color. Brow mascaras are available in a range of different colors and can be used to complement or blend in with the rest of your look.