How the hell do dermatologists tell the differences?

If you’ve ever looked at skin disease photos (YAR), it quickly becomes obvious that the bajillion things that can go kablooey on the skin not only tend to look incredibly similar to one another, they also look incredibly different on different people!

While there are very straightforwardly characteristic things like herpes, which form blisters first that then break and weep, so many other things just all blend together into what my mother would call Galloping African Crud. You gotcher redness, characteristic of 98% of skin issues. Then you got spots, raised spots, dry patches, weeping wet skin, flakiness.

Along with a few other broad categories of symptoms, dermatological issues are kinda like the Taco Bell of disease states: a few ingredients assembled in slightly differing ways.

So how complex and difficult/easy is it to learn to tell them apart, especially when they can’t be tested for?

Also, while we’re on the subject… what is it with “refillable” blackheads? I’ve had a blackhead/pore thing on my face for more than 30 years in precisely the same spot and no matter how many times I clean and squeeze, it refills within weeks or months.
(Anyone else start messing with their blackheads when they were super-young and had NO idea what they were and freaked out thinking you had worms in your face? I guess that was just me…)

Differential diagnosis is challenging in dermatology. But a careful clinical history and skilled observer (who is good at detecting subtle differences and evaluating anatomic distribution of lesions) can help quite a bit.

Then there’s the fallback of doing a biopsy, which may be helpful at subcategorizing lesions or rendering specific diagnoses.

BTW, herpetic lesions are not all that specific in appearance, and can be mimicked by a host of blistering disorders. A Tzanck prep (smear from the base of the lesion) often yields characteristic nuclear inclusions on microscopic examination.

Of course, you can always slather on corticosteroid cream and see what happens…

Ah yes, steroid-responsive vs. non-steroid-responsive rashes.

I’m reminded of The Four Axioms of Dermatology I learned in medical school:

  1. If it’s dry, wet it
  2. If it’s wet, dry it
  3. If you don’t know what it is, don’t touch it
  4. If you know what it is, you don’t have to touch it
  1. If they’re not on steroids, start them.
  2. If they are on steroids, stop them.
  3. Biopsy everything.


I see dermatological research has come a long way in the last 10 years. I’ll admit I haven’t focused on derm journals in my CME studies!


LOL, I learned those rules in the 1980’s. I was told then that those 7 things were all I’d need to know about derm.

A few years back, I went to my doctor for some reason, but also asked about with a rash on my legs. We discussed it for a while and he diagnosed it as Score (or so I thought actually it was SKOR). I asked him what that meant. He said he’d had the same diagnosis from his dermatologist and asked. The dermatologist said Some Kind Of Rash.

So yeah I think they’re just guessing often if it doesn’t appear to be a real problem.

Just a bump for the “refillable blackheads”. I’ve got a few of these–no matter how many times I squeeze 'em, they always come back in the same spot.

Then read the pathology report.

Yeah, the last time I went the weird dermatologist scraped off part of my chest and the fungus* attached to it and took it to the other room, for microscopy or mad chemistry.

Dermatology is an awesome job. Doctor without most of the rockstar perks (hot nurses?) but with less stress. Unless you get someone with Stevens-Johnson or something (do not google while eating). They probably go straight to the ER there, though.

*Tinea versicolor if you must ask. Ironically likely caused by being too clean.

I think the deal with those is that the underlying pore structure has been damaged.

There’s even an app now that scans the blemish and then compares it to an visual database.

Frankly, the path report only helps me maybe half the time.

The other half, it tends to just show non-specific inflammation of one sort or another. While it’s nice to say “it’s not cancer” in those circumstances, it still leaves the question open-ended.

My hat’s off to Derm docs, who can usually put all the clues together and find something that will help.

I had a pressing derm question for about 3-4 years, then it magically cleared up on its own. My GP said she had no idea what it was except that it wasn’t fatal, and I should see a derm. Lost my insurance before I could go.(Permanent bruised areas on my shins that were flaky and the flesh was hard underneath. I just noticed recently that they were finally gone after being there since about 2008)

Yeah, I guess some pores just get stretched and never bounce back, so they are vulnerable to ongoing sebaceous buildup… blegh…

IANAC (I am not a clinician), but If I was I would think ruling out The Big C would be a big help.

IANAPWADC,ATM (I am not a patient with a dermatological condition, at the moment), but if I was I would think finding out I did not have The Big C would be A big relief.

Glass half full/empty, I suppose.