I use a 1% hydrocortisone cream on areas of redness/irritation. I put it on in the morning after I take the mask off. It is not a product that should be used continuously or while you are wearing the mask. The hope is that you get used to the mask, and the cream is only a temporary measure to help repair the irritated skin until it toughens up.
I don't have any personal experience with them, but there is a range of mask liner products. See link below. Perhaps others can give you some recommendations on what works, and what does not.
Jeff, doesn't seem like a normal thing; haven't heard of anyone else having a rash under the whole area where you mask is. I am pretty sure there are different materials in masks made by different manufacturers. What type mask are you using? Perhaps a different mask might help get rid of the red face. Worth a try. Sounds like an allergy or sensitivity to that mask's material. You could try mask pads but if you are getting a red face where the mask cushion isn't sitting, the mask pads may or may not help. Look at a picture of one and cut out some cotton in the shape of the cushion and give it a shot before investing as the mask pads are generally kind of expensive for tee-shirt material cut in the rough shape of a mask cushion.
Are you new to CPAP? When I was new to this treatment, I put my mask on really tight. I was worried my pressures would blow the mask off my face. In the morning, my reward was a beautiful red mark all around my face wherever the mask touched the skin. I learned to loosen up a bit and let my worries go and things got much better.
Some people are actually sensitive to the mask seal and do wind up with the reddened, wind-burn-like skin wherever the mask touches the face. The mask liners really do help these folks. Mask liners have taken a step up from 6 years ago when I started on CPAP. They look like no loose fabric hangs out to brush up against the eyes. Much better. The ones I'm admiring are the Silent Night mask liners. I've never ordered them, but I had a good experience ordering an SD card and reader from this online vendor...cpapXchange.com and the ad for the liners came with my package. I have no idea how much they cost, but, as wiredgeorge has noted, they're all kind of expensive. This ad says the Silent Night ones are reusable, so maybe you can leave one installed on your mask for up to one week? That would make the price better!
While you're waiting for your liners to arrive, you might try washing your mask each night. I use fragrance-free biodegradable dish soap and rinse really well, then air dry. Let's see if this helps.
OK. Medical professionals have come across this. It looks a lot like rosacea (or wind burn), but is actually a sensitivity to the mask material. The reaction generalizes in some cases and that could be why a large portion of your face is involved. It's not from your treatment pressure. So, the liners might still be an answer for you, since contact with the skin might be what brings on your generalized reaction.
Probably the best thing to do is to bring this to the attention of your doctor along with further details, such as; whether the redness subsides throughout the day following your CPAP treatment, etc. If he/she wants to see you, make sure your appointment is for early in the morning so that you make the best presentation of your problem.