RecruitingPhase 3Drug trialA Histamine Pharmacodynamic Biomarker to Guide Treatment in Pediatric Asthma (HAS3)This is a randomized, double-blind, placebo-controlled, crossover study comparing asthma control post treatment in African American/Black and Caucasian/White children in both hyper and hypo responsive HILD (Histamine Lontophoresis with Laser Doppler monitoring) phenotypes with uncontrolled persistent allergic asthma using Levocetirizine (LTZ) vs placebo.