I have a red and itchy rash at the top of my buttock crack. There are no bumps. When I scratch, pieces of skin come off.

It sounds like you may have irritation in the area that is causing redness and itching. It is important not to scratch the area to avoid further damage to the skin. You can try applying a protective cream like petroleum jelly or zinc oxide ointment a few times a day. If the symptoms do not improve after a few days, there could be a fungal infection, and you may need to use an antifungal cream available over-the-counter. It's best to consult a healthcare professional if the issue persists for proper diagnosis and treatment.