This is a calorie free way to indulge in chocolate! Let your skin drink up the skin benefits that cocoa has to offer. Cocoa is rich in antioxidants; specifically, the category called flavanols. These have been studied and linked to assisting in protecting the skin from UV rays, due to the properties in flavanols. 
Also present in cocoa, is theobromin. This is known to increase the flow of blood to the surface of the skin. This increased blood flow could stop the skin drying out in the way it characteristically does when you get sunburnt.