Oxidizing milk developer primary step in skin sensitivity test; clean a small portion in elbow, using a cotton swab. dab a small amount of the mixture to the area. leaved uncovered for 24 hours. if skin irritated, redness occurs wash immediately with clean water. do not proceed with hair colour application... primary step in skin sensitivity test; clean a small portion in elbow, using a cotton swab. dab a small amount of the mixture to the area. leaved uncovered for 24 hours. if skin irritated, redness occurs wash immediately with clean water. do not proceed with hair colour application...