Which of the following should be avoided to maintain skin integrity under a cast?

Maintaining skin integrity under a cast is crucial for preventing complications such as skin irritation, sores, or infection. Sticking anything under the cast is particularly harmful because it can lead to trauma to the skin, disrupt blood flow, and introduce bacteria, all of which can increase the risk of skin breakdown and infection. The skin underneath the cast needs to remain protected and free from foreign objects that can cause irritation or injury.

Using lotion on the cast can sometimes be permissible for keeping the skin moisturized, provided that it does not interfere with the cast's integrity or its purpose of immobilization. Scratching the skin could lead to damage and opens the door for infection; however, it does not apply under the interpretation of the key preventative measures for preserving skin integrity in the same direct manner as inserting something underneath the cast.

Therefore, avoiding sticking anything under the cast is the best practice for maintaining skin integrity.