One easy way to tell if a rash is serious

The Pediatric Insider

© 2012 Roy Benaroch, MD

Rashes are tough to diagnose over the phone. Even if you MMS me a pic, I can’t really feel it or get an overall gestalt of what the child and the rash looks like. (And, of course, MMS isn’t HIPAA compliant. Heaven forbid the gummit allow us to do something that might be easy, cheap, and helpful.)

Most rashes can easily wait a day or two for diagnosis. In kids they’re often triggered by mild viral infections, and the rash will go away on their own without therapy. Itchy things like eczema or poison ivy or contact derm get better with over-the-counter hydrocortisone.

On the other hand: some rashes, especially if accompanied by fever, can be a warning sign of a potentially catastrophic condition. Meningitis, sepsis, and leukemia can all present with a rash.


So, here’s one good, middle-of-the-night way of helping parents decide if a rash needs immediate attention:

As always, the posts and comments on this blog are general info to educate and inform. I am not your doctor, and this is not specific medical advice for your individual situation. If you’re worried, contact your own doctor directly. Also, the following info is only for healthy, ordinary kids who have been fully vaccinated. If your child has chronic health issues, immune problems, or is under-vaccinated, he is at much higher risk of serious complications.

Step 1. Does the child seem OK? If your child has a rash (or even if he doesn’t have a rash), your first question is: does he seem very sick? If Junior is hard to wake up or very pale or grey-looking or having trouble breathing or just doesn’t seem right, get thee to the nearest ER, pronto. Don’t mess around with the internet, and don’t mess around with trying to figure out what a rash means. Very sick-seeming child = trip to ER. Go.

Step 2. If your child with a rash seems reasonably well, but maybe blah with a fever, treat the fever first. The fever itself is not harmful, but it will make your child feel bad. Once the temperature starts to come down, you’ll be able to re-assess just how sick your child is. A vaccinated, healthy child who’s comfortable and playing after fever reduction is very unlikely to have anything seriously wrong with him, and almost certainly doesn’t have to go to the ER or see a doctor immediately.

Step 3. Assuming your child seems reasonably well, let’s see if this really is a rash that needs immediate evaluation:

Take a thick glass or a tumbler, and press the side of the glass against the rash. Peer through the glass at the skin. If the rash disappears with the pressure of the glass, it’s unlikely to be anything serious. If the rash can still be seen through the glass, it could well be a serious rash called “petechiae” or “purpura”, which is bleeding under the skin. Though petechaie are not always a serious problem, it can be. Contact your doctor or go to the ER if your child has these kinds of rashes that don’t disappear with the pressure of a glass.

One caveat: vomiting or coughing or straining hard can cause a little bit of petechiae on the upper face or around the eyes. Don’t worry too much about that. But widespread petechiae do need attention.

That’s all it is: the “tumbler test”, a quick and easy and cheap way to diagnose the most-concerning rashes of childhood. We’d better keep this quiet, or some drug company will start selling a sterile one-use shot glass for $600. It’ll be FDA-approved, as long as you don’t take a picture of it to text to your doctor.

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4 Comments on “One easy way to tell if a rash is serious”

  1. (Another) Becky Says:

    This information is so important. I only knew about this because Dr. Laura Nathanson mentioned this rash a few times in her book The Portable Pediatrician. If I recall correctly, it also tends to be purpley red instead of pink. I noticed a rash like this on my daughter when she was about 20 months old. It concerned me although it was only on a small area when I first noticed it, so I called the on call pediatrician for my doctor’s office. She brushed it off as worry (despite the fact that it was my third child) and told me to put lotion on it. Because I knew how serious from the book how serious it might be, I then called the insurance nurse hotline, which was far more helpful than the doctor, and who told me to take my daughter to the ER. The rash was STILL not treated as serious and we had to wait for a quite a while. When we finally saw a doctor, he took one look at the rash, said “That is not what I expected to see” and admission proceedings were begun immediately. Luckily, it was only ITP and not something like leukemia. Still, she was in hospital for three days until her platelet count came back up.

    If I hadn’t been informed about how serious it could be, I would have followed the doctor’s very erroneous advice.


  2. Brenda Says:

    My ten month old had a purple rash with virul symptoms been to nhs 24 they looked at her and said it’s virul but I’m not convinced , what do you think ? It does not disappear with glass test


  3. Cris Says:

    Thank you!! This information was very helpful!

    Liked by 1 person

  4. Sarah Says:

    I had a similar situation with my 6 month old. He had a fever of 105 for 3 days, then developed a rash, blood shot eyes, and wasn’t eating. They told me it was a virus. It being my first I had no idea so I just assumed they were right. By day 4 and 5 and then 6 going back 2 more times with the same result, I knew I wasn’t crazy and something was very wrong. He ended up having kawasaki disease and was finally treated during a 5 day stint in the hospital. Thank God for good doctors who listen to the sobbing mother when she tells them she knows something is wrong.

    Liked by 1 person

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