Do you have a rash? Know the difference between common conditions and when it could signal a more serious health concern.

Rashes are caused by exposure to any number of environmental allergens such as food, weather, sunlight and even stress.

Many of these can be treated effectively with over-the-counter medications. But in some cases, your skin may be telling you that you have a more serious condition.

“In dermatology we treat a wide variety of rashes from life threatening to simply bothersome,” said Ashley B. Crew, MD, assistant professor in the USC Department of Dermatology at the Keck School of Medicine of USC.

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Because your skin is the largest organ in the body, it can show signs of an internal disease before the disease shows typical symptoms.

When a rash is more than a rash

A minor rash is easily treatable with antihistamines or hydrocortisone cream. But you should speak with your doctor if you have any of the following symptoms.

  • Do you have a fever or pain accompanying your rash? It could be a sign of infection and should quickly be evaluated by your doctor.
  • Do you have blisters? A rash that begins to blister but that can’t be explained by exposure to poison oak or ivy could be shingles.
  • Does your rash persist without improvement from over-the-counter medications?
  • Is there any bruising or swelling around it? The rash may be preventing proper blood flow.
  • Is there any discharge or secretion from the rash? Any colored discharge or bad odor is a sign of infection.
  • Did the rash appear and spread quickly? This could be an allergic reaction to medication or food. Seek immediate medical attention if breathing becomes difficult.
  • Is the rash circular in shape? This could be a sign of Lyme disease.
  • Do you have skin discolorations or changes in your skin texture? A yellowing of the skin could indicate liver disease. Hardening and darkening of the skin could be signs of diabetes.

Common adult rashes

If you have ever had the chicken pox or been vaccinated against chickenpox, you are at risk of developing shingles later in life.

Shingles are reddish patches of skin with small bumps that blister and itch. Pain can be moderate or severe, lasting up to five days and taking up to four weeks to heal.

When your immune system is weakened, perhaps by something as simple as a cold, the shingles virus can infect your skin cells. Typically, you will feel tired before the rash appears and might experience a mild fever.

Hives appear as a rapidly spreading, red-raised and itchy rash in splotches or all over the body. Caused by an allergic reaction to medications and food, hives can be a sign of a life-threatening problem when accompanied by difficulty breathing and a drop in blood pressure.

Allergic reaction to medications
Rashes can develop from an allergy to a medication, also known as DRESS syndrome (drug reaction with eosinophilia and systemic symptoms). This condition may take weeks to appear after you start a new medication. Common symptoms that accompany the rash are fever and inflammation in the liver, heart, lungs or thyroid.

“Some of the rashes we see are dangerous because of the rash themselves,” said Dr. Crew, who also is a dermatologist at the USC Department of Dermatology at Keck Medicine of USC. “An example of this is a severe drug eruption called Stevens Johnson Syndrome or Toxic Epidermal Necrolysis, where people develop sudden peeling skin and mucosal surfaces.

“Other serious rashes treated by dermatology can be dangerous because they signify other underlying issues — examples of this include a cutaneous vasculitis or lupus rash.”

Rashes can be indications of a more serious problem. If you are unsure of the type of rash you have or if it is taking days or weeks to heal, seek help from one of the dermatology experts at Keck Medicine of USC. If you are in the Los Angeles area, make an appointment by calling (800) USC-CARE (800-872-2273) or by visiting

By Heidi Tyline King