Viral Skin Infections - Causes and diagnosis

How do I know which virus has caused my rash?

To be honest, it's usually not important to know the exact name of the virus. And often a doctor just won't know. Blood tests can only detect some viruses, and even then they are quite slow tests, often taking a few weeks to come back.

There are a few conditions where a virus is known to cause a specific skin condition.

  • Chickenpox is caused by varicella zoster. (This virus can lie dormant in your body and then come out years later as shingles.)
  • Pityriasis rosea is caused by a type of herpes virus.
  • Hand, foot and mouth disease is caused by Coxsackievirus and enterovirus.
  • Mumps and measles are caused by the mumps and measles viruses (the virus and the illness have the same name).
  • Molluscum contagiosum is caused by pox virus.
  • Orf is caused by parapox virus (which starts off in sheep or lambs).
  • Herpes simplex is caused by the herpes simplex virus type 1 (this is the same virus that causes cold sores); however, genital herpes is caused by herpes simplex type 2.

How does a doctor diagnose a viral skin condition?

  • Usually a doctor can tell what the skin condition is, by what you tell them and by what it looks like.
  • Very occasionally if there is an unusual skin problem that the doctor can't work out, they may refer you to a doctor who specialises in skin conditions (a dermatologist).
  • If a rash looks like mumps or measles then sometimes a doctor will give you a blood test. This is just because it can be important to tell if you've definitely had measles or mumps in case there's an outbreak somewhere, like a school.

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Dr Oliver Starr
Peer Reviewer:
Prof Cathy Jackson
Document ID:
29415 (v1)
Last Checked:
23 July 2017
Next Review:
22 July 2020

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. Patient Platform Limited has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.