Study of Prophylactic Topical Dapsone 5% Gel Versus Moisturizer for Cetuximab-induced Papulopustular (Acneiform) Rash in Patients With mCRC or HNSCC Without Previous or Concurrent RT

The purpose of this study is to see if the investigators can prevent or reduce the severity of the Cetuximab-related acne rash. Two different topical agents will be applied to the skin. One topical agent is the dapsone gel and the other is a skin moisturizer. Dapsone gel is an FDA approved medication that you apply to the face. It is commonly used to treat acne. Skin moisturizers are recommended to patients who receive Cetuximab treatment. In addition to these topical agents they will be given a pill to take once a day. This pill has already been shown to help fight rashes from Cetuximab.