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Pityriasis rosea is a common skin condition that affects 0.15% of the general population. The condition often occurs in older children and young adults between ages 10 and 40 years and is rare among elderly and infants.
The condition has been described for more than two centuries and has a characteristic rash that begins with a small patch called the “herald patch”. This is followed by spread of a red, scaly, itchy rash to the chest, back, arms and legs. Women are at a slightly higher risk of this condition. 1-7
The exact cause of this condition is still unknown. There are certain factors that lead to the belief that this may be caused by a viral infection.
The reasons for this belief is that pityriasis rosea tends to occurs in epidemics and affects large groups of persons together in a community especially during spring and autumn seasons. This could mean an infectious agent is responsible for the condition. In addition, recurrence is rare and this means that persons getting the rash may develop long lasting immunity to the infectious agent responsible for the condition.
Another significant sign that there could be an infectious agent behind pityriasis rosea is that more than 50% of the patients have some symptoms of feeling unwell before the appearance of the herald patch. This precedence of rash with general feeling of being unwell (termed prodromal symptoms) is common in cases of other viral infections. The course of the disease is also well defined and similar for most affected persons and follows a pattern much like other viral infections like measles or chicken pox.
In addition, some patients also show an increase in B lymphocytes and a decrease in T lymphocytes along with increase in Erythrocyte sedimentation rate (ESR). Lymphocytes are white blood cells that fight against infections so their rise is also significant. In addition, many infections show a rise in the ESR.
Some studies have suggested that a virus may be causing pityriasis rosea. When seen under an electron microscope viral changes and virus particles have been noticed. However ,blood tests for antibodies against the viruses or special tests like polymerase chain reaction for viruses have not been positive to pinpoint a specific virus causing the condition.
Some studies have implicated Human Herpes Virus 6 and 7 in causation of pityriasis rosea. Other infections that need to be considered as causative agents of this condition include Legionella pneumoniae, Chlamydia pneumoniae and Mycoplasma pneumonia. However, these have not been proved.
Studies have suggested that some drugs may lead to drug-induced pityriasis rosea. These include:
Despite these speculations, and occurrence of the rash in more than one person in a household at a time and more than one person in the community at a time, the disease is not contagious and does not spread from one person to another by touching.