Unstageable means nobody can tell how deep it is yet, because something is covering it.
It’s one of two types of pressure sore that don’t fit into the four stages: sores covered in dead skin that is yellow, tan, green, or brown. The dead skin makes it hard to tell how deep the sore is. This type of sore is unstageable.
So it isn’t a fifth stage, and it isn’t a measure of severity. It’s about what can be seen. The wound has a depth; it just can’t be measured through the covering.
That matters because staging drives everything else. The four stages decide whether a sore is usually managed at home or by a provider, and what the outlook is. A sore that can’t be staged can’t be placed on that scale until the covering is dealt with.
Removing the covering isn’t automatic. Debridement (removing dead tissue) may not be appropriate for dry and intact eschars with no clinical evidence of infection underneath. One example is an unstageable pressure ulcer with an intact eschar at the sacrum, buttock, or heel. The intact eschar serves as a natural covering over the damaged skin underneath.
That’s why a dark, hard area on a heel may be left in place on purpose while another wound is debrided. It’s a decision, not an oversight. Whether it applies depends on whether the eschar is dry and intact and whether there is evidence of infection underneath, and that’s answered by an exam, not by looking.
When it comes to debridement in general, you should never try to do this yourself.