8.3.2.3　Drug concentration

In general，enhanced drug concentration will increase the transdermal efficiency.However，some drugs have obvious skin irritation effect or coagulation effect on keratin at high concentration，which reduces skin permeability and results in poor drug absorption.In addition，the concentrations are related to the solubility of drugs.To achieve an ideal transdermal efficiency，a drug is generally supposed to possess a solubility above 1 mg/mL both in water and oil.(https://www.daowen.com)