Why does the Tecnu label say it cannot be used with hydrocortisone for three days?


You can use Tecnu before using a hydrocortisone ointment.  Just make sure to wait at least 3 days after using a hydrocortisone ointment, before using Tecnu.

The reason is that the use of hydrocortisone thins the skin, allowing any topical application to the skin to penetrate more readily.  If you are slightly sensitive to a detergent, like Tecnu Original Outdoor Skin Cleanser, it will aggravate the skin more quickly and severely.

Tecnu Original uses