Maybe this is how you get readers to open a post in this forum ; )
For those interested the whole article, it's at --> BMJ Case Reports 2014; doi:10.1136/bcr-2014-203975; Cutis marmorata marbling in an individual with decompression illness following repetitive SCUBA diving; Michael M Modell.http://casereports.bmj.com/content/2014/bcr-2014-203975/F1.large.jpg
Figure 1 -- Cutis marmorata marbling (left gluteal) occurring in a 49-year-old female self-SCUBA diver with decompression illness.
BTW, the diver also developed signs/symptoms of neurological (Type II) DCS & was found to have a PFO.
As for differentiating cutis marmorata v an allergic reaction or other topical/contact dermatitis, cutis typically is a marbled/mottled/bruised-looking violaceous rash with some very slightly raised areas, but typically is without distinct small red bumps or hive-like elevations (for another female cutis buttock photo, see below*1). Allergic rash typically is reddish to scarlet with distinct raised red bumps, but without clear marbling/mottling (see img *2). Once you've seen both, it's easy to distinguish them.
If a diver has ONLY cutaneous DCS, it will clear w/o treatment, usually within a couple of hours and almost always no longer than 24 hrs. It usually is harmless, although it does with some frequency indicate the presence of PFO. As such, if a diver has more than an isolated incident of mild cutis it is best to follow up with a diving medicine cardiologsit to elaulaute for this possibility.
The real worry is that in about 20% of cases the cutis rash heralds (if not already accompanied by) the coming of more serious signs/symptoms, such as neurological DCS (Type II). I have images of a young man who presented with a cutis rash on his back who went on to die of Type II DCS complications about 12 hrs later despite the fact the he received recompression treatment. It is primarily for this reason that a diver who presents with potential skin bends should immediately be placed on 100% O2 & medically evaluated