By Caroline Kee -
Today
When you press on your skin for a few seconds and then remove your finger, does that area appear lighter?
That phenomenon is called blanching, and some social media users are using it to determine if a child's rash requires medical attention.
But can this test really tell if a rash is serious or not?
This is what the experts think.
What is a "bleaching" test?
"Bleaching occurs when the skin loses color due to blood moving away from where pressure is applied," explained Dawn Davis, a professor of dermatology and pediatrics at the Mayo Clinic in Rochester, Minnesota.
"If I press on my skin and it looks slightly pale when I release my finger, it's because
I've temporarily pushed or stopped blood flow to that area
," she added.
In medicine this is called "diascopy" and it consists of taking a glass slide, like the one in a microscope, and pushing it over the lesion or reddened skin to see if it disappears with pressure and determine what type of rash or lesion it is. .
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This can also be done at home with a glass cup, which makes it easier to see the skin where pressure is applied, said Adam Friedman, professor and chief of dermatology at the George Washington University School of Medicine and Health Sciences. .
"You just have to be careful when applying pressure so you don't break the glass on your skin, it's happened before," he warned.
Why do some rashes “whiten” and others don't?
“When an area of the skin is red it is because the blood vessels are dilated or widened and there is more blood flow,” Friedman explained.
When a rash "clears up" it's because the redness goes away with pressure,
but it comes back because the blood is still inside the vessels and just moving around, he added.
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If a rash doesn't get "pale" it means
there is bleeding or blood leaking from vessels under the skin
(also called
purpura
) that can be caused by a variety of conditions, Friedman said.
"If the blood is outside the vessels, the skin will not turn white (because) it does not move."
When an area of the skin is red it is because the blood vessels are dilated or widened and there is more blood flow”
Adam Friedman, PROFESSOR of dermatology
Rashes or discoloration may look different depending on skin color.
“'Bleaching' darker skin, and even recognizing that there is redness, is more difficult,” Friedman stressed.
What may appear red or violet-toned on fair skin may appear brown, black, or even off-white on darker skin.
“Being able to distinguish that paleness might require more pressure,” she added.
What causes these rashes?
“People often think that if something clears up, it means it's not harmful, but that's not true,” Davis warned.
An extreme "whitening" of the skin can occur due to a lack of circulation caused by frostbite or Raynaud's phenomenon, which occurs with cold.
“Blood vessels constrict due to illness or temperature changes, and that can leave the tips of your fingers or toes white,” Davis said.
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Another "clearing" rash is one that occurs when blood vessels, which are usually benign and harmless, are broken or dilated.
This is known as
telangiectasia
, Davis said.
“However, there is not always consistency between something being bleached or not and being benign or harmful,” he explained.
Sometimes
telangiectasia
is a sign of a more serious internal disease.
“In the early stages of
vasculitis
(inflammation of blood vessels), which can be very damaging, many lesions blanch because there isn't enough inflammation or destruction yet for blood to leak through,” Davis said.
If the child or adult feels lethargic, intoxicated, or has an acute fever, that would require urgent attention.”
Dawn Davis, PROFESSOR OF DERMATOLOGY AND PEDIATRICS
Allergic reactions and insect bites can also cause blanching rashes, Friedman explained.
"If someone develops hives or welts, which can be the result of a food or medication, sometimes they clear up," she said.
Hives are not dangerous, but when accompanied by symptoms such as wheezing or difficulty breathing, it can be an emergency.
"It all depends on what accompanies the eruption," he
added.
There are many skin lesions that, along with systemic features -- such as fever, joint pain, organ failure, diarrhea or vomiting -- are an emergency, Friedman said.
"There are many life-threatening drug reactions that present a blanching rash that should not be ruled out," he warned.
Are these rashes serious?
There are many causes, some more serious than others, behind a "purpuric" rash or bleeding under the skin, Friedman said.
Meningitis can cause a rash that does not clear up, as can other bacterial infections such as
meningococcemia
and
gonococcemia
.
“(These) are actually a systemic infection that manifests itself in the skin due to the spread of that bacteria through the blood,” he explained.
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Purpuric
rashes
or vasculitis can also be caused by viruses such as hepatitis C, autoimmune diseases and even certain fungal infections in immunocompromised patients, he said.
"In these cases you don't just have this (non-blanchable rash) on its own, patients will have other symptoms," Friedman said.
These worrying scenarios are relatively rare.
Experts recommend watching for other signs and symptoms if you have a rash. Yuliya Shevtsova / EyeEm / Getty Images/EyeEm
Symptoms of meningitis include high fever, stiff neck, severe headache, confusion and vomiting, according to the Mayo Clinic.
The texture of a rash that doesn't clear up can also offer clues.
"If you have what's called palpable purpura, which is a nonblanchable rash that you can touch, our mantra in dermatology is that it's vasculitis until proven otherwise," Friedman said.
"With vasculitis there is inflammation that attacks the vessels until they are damaged or even destroyed," he said.
This can be the result of serious drug reactions and malignancies (cancers).
If vasculitis is suspected, he suggests testing to identify the cause.
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Some "unbleachable" rashes are not dangerous.
One of the most common is the so-called benign pigmented purpura.
Others are solar purpura, which looks like violet-colored spots that often appear on sun-exposed areas in older people, and bruises or broken blood vessels from other activities.
“They are annoying, but benign,” he added.
Although not all rashes are an emergency, "it never hurts to get checked out," he recommended.
Always be on the lookout for any other symptoms.
Is the test promoted in networks reliable to determine if a rash is serious?
The short answer is no,
you can't tell if a rash is malignant or serious based on whether or not it turns pale
when pressed
alone , Davis said.
Although it can help identify what type of rash you have, it is not a diagnostic test.
"You have to distinguish between whitening and non-whitening, but then there are other features that need to be clarified to determine if it's just a rash or it's a rash associated with something else," Friedman suggested.
Both experts recommend watching for other signs and symptoms if you have a rash.
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One of them is fever.
"
I think a fever and rash should always prompt some investigation
and a fever with a rash that doesn't clear up is even more concerning," she said.
"If the child or adult feels lethargic, intoxicated or has an acute fever, that would require urgent attention," Davis warned.
Another important aspect is how the rash spreads.
"If it progresses unexplained it could be more of a concern and you should seek a doctor's evaluation as soon as possible," she said.
"Anytime a rash develops, whether it's an adult or a child, it's helpful to be aware of your overall health at the time," Davis recommended.
“
Because the skin is often the window to the overall health of the body
.”
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