"Although fexofenadine is devoid of CNS effects, many other second-generation H1-antihistamines still penetrate the brain to a small extent where they have the potential to cause some degree of drowsiness or somnolence, particularly when used in higher doses."

source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3667286/

Second-generation H1-antihistamines are at least partial substrates of ABC-export pumps in the blood brain barrier,e.g., of p-glycoprotein. Their penetration across the barrier is the better, the lower the affinity to the export pumps.