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How can you tell if a rash is serious? Look for these signs

Red, itchy rash? If it comes with other symptoms, it could indicate something serious.
One important rule of thumb is to seek help if the rash came with other symptoms.
One important rule of thumb is to seek help if the rash came with other symptoms.Getty Images
/ Source: TODAY Contributor

The itchy red bumps came out of nowhere and it's unclear whether the mystery rash is something that needs a doctor or if it can be soothed away with over-the-counter salves. And with summer in full swing, it's open season for rashes.

“There’s a lot more opportunity to get into stuff that would cause a rash if the weather is nice,” Dr. Carolyn Jacob, a dermatologist in private practice in Chicago, previously told Culprits include everything from the sun and hot temps to brushes with plants and insects.

While it might be hard to pinpoint what is causing skin redness or itching, but contact dermatitis can be a common allergic reaction to skin care products. As it turns out, plenty of rashes respond well to over-the-counter remedies.

But some are a sign of something more serious, experts say.

When to seek to medical help

One important rule of thumb is to seek help if the rash came with other symptoms.

“The majority of rashes are not life threatening,” said Dr. Daniela Kroshinsky, an associate professor of dermatology at Harvard Medical School and director of inpatient dermatology and pediatric dermatology at Massachusetts General Hospital.

“But, if you’re feeling generally unwell and having a rash, that would be a reason to seek medical attention. Your primary care physician or dermatologist should be able to help you triage whether it’s something that should be seen and whether it needs to be seen urgently.”

A rash can be a warning sign of a serious medical problem, such as an autoimmune disease or a Lyme infection, explained Dr. Laura Ferris, an associate professor of dermatology at the University of Pittsburgh Medical Center. Or it could simply be the result of a harmless, though vexing, insect bite or a brush past some poison ivy.

How can you tell if a rash is serious?

Here are some signs that your rash needs to be looked at by a medical professional:

1. If you have a fever or pain accompanying the rash.

You should get it checked out, Kroshinsky said. It could be a sign that you have an infection or are experiencing an allergic reaction.

2. If you have a sudden spreading of bruise-like lesions.

It might be a symptom of vasculitis and you need to get that looked at because your clotting cells might not be working right, Kroshinsky explained.

3. If your rash continues unabated.

You might have an infection, Kroshinsky said. “Some rashes start out completely benign, but then a secondary infection develops because the integrity of the skin, which is a barrier against potential pathogens, has been disrupted,” she explained. “Signs of an infection include warmth and pain, yellow or green cloudy discharge and a bad odor.”

4. Any rash that is widespread.

It can be a sign a major allergic reaction. “For example, if this happens within two weeks of starting a new medication, the concern would be a reaction to the medication,” Ferris said.

5. Rashes that start to blister should send you straight to the doctor’s office, unless you have good reason to suspect you’ve come in contact with poison ivy, both experts noted.

Poison Ivy rash and blisters on a leg
Poison Ivy rash and blistersAlamy

6. Purple spots that appear on your hands and feet could be a sign of a bacterial infection of the heart, Kroshinsky said. “You can look at the skin as a window to the inside of the body,” she explained.

7. If you develop a circular-shaped rash and you’re in an area where Lyme disease is endemic, you should get it checked out, Ferris said.

If you’re not ready to see your doctor, Kroshinsky suggested taking a photo of your rash.

Lyme disease patient with characteristic bulls-eye rash.
Lyme disease patient with a characteristic bulls-eye rash.Alamy

“It can be helpful when you come in to see us since the rash could have changed by then,” she explained. “This will tell us what it looked like before you started treating it with bacitracin or hydrocortisone. It will help us get a sense of the evolution of the rash.”

Certain remedies and treatments can make a rash worse

Also, Kroshinsky counseled, keep in mind that the preparations you use to treat your skin condition might make things worse.

“One thing to keep in mind is that if you’re using a preparation with topical antibiotics, a significant number of people are allergic to bacitracin and neomycin,” she explained. “If the area you are treating becomes itchy or blistery you might want to stop using them and see a doctor.”

And if you feel unsure about the rash, don’t hesitate to seek medical advice from a dermatologist, Ferris said.

“We’re trained to distinguish between concerning and non-concerning rashes and getting you on the appropriate treatment,” she added.

Unsure if it's a rash? Use our photo guide to spot common (and not-so-common) skin conditions.