Hair not as thick, full and lush as you'd like. Give it a little extra oomph with Thick Again. The leave-in thickening treatment is designed for those with fine or thinning hair, and is rich in essential ingredients that will help thicken the hair and prevent breakage. Using breakthrough eyelash thickening and lengthening technology, they have harnessedingredients that will leave your hair looking thicker and fuller over time.