Pharmacokinetic Study of Topical Phenylephrine

Inclusion Criteria: * Healthy females, age 18-55 * BMI: 18-30 kg/m² * Fitzpatrick Skin Types I-IV (to standardize absorption risk) * Scalp free from irritation, dermatologic disease, or damage * Able to refrain from using other topical scalp products Exclusion Criteria: * History of cardiovascular disease, hypertension, or arrhythmia * Scalp infections, wounds, or significant hair loss * Recent use of medications that interfere with CYP enzymes or adrenergic systems * Known sensitivity to phenylephrine or ethanol * Positive drug screen or abnormal ECG at screening