Stage 1 -- redness of the skin that doesn't go away
stage 2 -- the skin surface is eroded
stage 3 -- the skin is eroded through down into the fatty tissues.
Stage 4 -- the fatty tissue has been eroded through and now muscle or bone is involved.
An early (acute) pressure sore may have dead tissue in the wound and may be "unstageable." an older sore may have pink or red tissue in the wound.