Keywords: Ala; alanine; Azone; N-dodecylazepan-2-one; DDAIP; dodecyl 2-(dimethylaminopropanoate); DDAK; dodecyl 6-(dimethylamino)hexanoate; ER; enhancement ratio; Gly; glycine; HC; hydrocortisone; IR; infrared; PBS; phosphate-buffered saline; PG; propylene glycol;