The preparation may cause serious inflammation of the skin in some persons, and a preliminary test should always be made to determine whether special sensitivity exists.
To make the test, a small area of skin behind the ear or on the inner surface of the forearm should be cleansed, using either soap and water or alcohol, and a small quantity of the product as prepared for use should be applied to the area and allowed to dry.
After 24 hours, the area should be washed gently with soap and water. If no irritation or inflammation is apparent, it may be assumed that no hypersensitivity to the product exists. The test should be made before each application.
Lack of reaction to this test does not guarantee that an allergic reaction will not occur later on.