The pit does not have any magical properties. What turns the guac brown is the air. If you can keep air from touching the guac then it will stay green. The pit will keep a portion away from the air, but what is more affective is to put plastic wrap over it and push it right down onto the surface.
Denuded skin is just another way of saying that the top layer (epidermis) of skin is gone...either from friction (abrasion or tear), trauma (tape burns), or severe rashes, or from a stage II pressure ulcer.
According to Wrong Diagnosis one of the causes of head pressure can be a sinus infection. Sinus infections are very common throughout the year, with an estimated 37 million cases every year. Often they start out with a stuffy nose, but symptoms depend on which sinus cavity is infected.