The dry rash that you have on your penis can be due to
seborrheic dermatitis.The main treatment of
seborrheic dermatitis is corticosteroids and shampoos containing ciclopiroxolamine, ketoconazole, selenium sulfide, or zinc pyrithione(like in antidandruff shampoos). In cases where steroids are not working,low doses of Accutane (Isotretinoin) are helpful.But it should be taken only after prescription from a dermatologist.