Sometimes, a rash is a sign something serious is going on with your body. It’s a good idea to keep an eye on any rash you develop and watch for these signs. Seek medical care if any of them develop.

1. You have a fever

A fever is a key sign that rash should be looked at by a doctor. It could be a sign of an allergic reaction. A fever along with your rash could also indicate an infection such as:

  • herpes
  • measles
  • mononucleosis
  • scarlet fever

2. The rash is spreading

A rash that is spreading is another sign it’s time to seek medical care. A rash that is spreading quickly might be a medical emergency. It’s best to go to an urgent care center or the emergency room if your rash is spreading rapidly.

If your rash is spreading slower but is spreading over your body, it’s still a good idea to get it looked at. It might be a warning that your rash is caused by an allergic reaction or an infection.

3. The rash area hurts

A painful rash should be looked at by a medical professional. It could be infected or a sign of conditions such as shingles.

It’s best to also keep an eye on any rash that isn’t painful but that is tender when you press on it. This could be a sign of infection, and you’ll want to have it checked out if it doesn’t resolve after a day or so.

4. The rash came on suddenly

A rash that comes suddenly may be an allergic reaction to a medication. Sometimes, a rash can develop in the first few weeks after you start a new medication. Let a medical provider know about this side effect as soon as possible.

It’s important to be careful when a rash is caused by an allergic reaction to mediation. This kind of reaction can lead to difficulty breathing and may become a medical emergency.

5. The rash is beginning to blister

Sometimes rashes caused by sun exposure or poison ivy can blister. These rashes generally heal on their own in most cases.

However, unless you’re sure your rash was caused by the sun or poison ivy, any rash that blisters should be looked at by a doctor. It could be a sign that your rash is a severe allergic reaction to a medication or caused by an autoimmune condition called pemphigus vulgaris.

6. You see signs of infection in the rash

Rashes damage the surface of your skin. This can make it easy for infections to develop, especially if you scratch the rash area. An infected rash should be looked at by a medical professional. Signs a rash is infected:

  • pain
  • warmth
  • swelling
  • crusting over of rash bumps
  • yellow discharge
  • green discharge
  • a bad smell

7. You have difficulty breathing

This is a medical emergency. Call 911 or seek care right away. A rash and difficulty breathing can be signs of a serious allergic reaction. This might happen when you eat or drink something you’re allergic to.

8. The rash looks like large purple patches

A rash that looks like large purple patches or dark bruises can be a sign of a serious condition. It could be a warning sign of an infection spreading throughout your body or of a blood clotting problem. It could also indicate a condition called vasculitis that causes your blood vessels to become inflamed.

A medical professional can determine what’s causing this rash and start treatment.

9. Bruises are forming in or around the rash

A rash with bruising or swelling around it might have been caused by an insect bite. It’s a good idea to seek medical care if you notice this symptom. The bruises and swelling are a warning that that poison from the bite could be cutting off blood flow to the area.

10. The rash is in a circle shape

A circular-shaped rash could indicate Lyme disease. Caused by ticks, Lyme disease normally causes a rash that resembles a bull’s-eye and symptoms similar to the flu. Antibiotics are the primary treatment for Lyme disease, so you’ll need to visit a medical provider for a diagnosis and prescription.

11. You’ve had the rash for longer than a week

A rash that persists for more than a week is worth getting looked at by a medical professional. There might be a reason your body is having trouble healing the rash. Plus, even if your rash is mild, a medical professional can give you tips to treat it at home.

12. The rash is causing you discomfort or concern

It’s a good idea to get any rash that is causing you to feel significant discomfort or concern checked out by a dermatologist or other healthcare professional. While it might be simple contact dermatitis, it’s still a good idea to consult a doctor.