Sores, redness and bumps around your nose can be caused by one of three main reasons: facial oils are building up under the mask material; the mask is overly tight; or the mask material is causing an allergic reaction.
A breakout can occur from the facial oils building up under the mask at night. You can help minimize this by washing your face before putting on the mask at night and by cleaning the facial oils off the mask every morning. If you are still experiencing a breakout, you might consider Nasal Pillow Mask which have less material that comes in contact with the skin.
Sores at the bridge of the nose or below the nose are usually due to tightening the headgear straps too much. The pressure will create soreness, then a bruise, and may eventually create an open sore if left untreated. Your mask should seal when worn comfortably. If you have to over tighten your mask to get a good seal, consider switching to another mask type. To avoid over tightening your mask, you should work clockwise around the mask, making small adjustments to the headgear, until the headgear in securely in place but not overly tight. You should avoid pulling too much on one side of the mask than then other.
Most masks are made of silicone, which is an inert substance. But silicone is manufactured in chemicals to which some people are allergic. The chemicals normally degrade and disperse over time, but may cause a reaction when first used. The solution is to remove surface chemicals before using the mask. Washing the mask will reduce or eliminate the problem. This process can be accelerated by long soaks in warm soapy water. This method can be used with all types of masks, and should also be applied to mask replacement parts. While soaking the mask will help remove the surface chemicals, it my reduce the life of the silicone.