Pityriasis rosea is not an allergic condition but is frequently seen by allergists as its main manifestation is a skin rash that looks “temptingly allergic” in nature.
This rash is preceded by a single spot called the “herald patch.” This clue is sometimes missed because it appears in a hidden spot on the body such as the back or armpit. Within one to two weeks of the herald, a generalized rash appears.
The spots are circular to oval in shape and about the size of a mosquito bite. There tends to be a little scaling of the skin from the pink/red spots.
On the trunk the rash often resembles a “Christmas tree” in distribution. It can occur at any age but is most common between 10 and 35 years of age.
Most patients don’t feel any sensation from the rash, but 10-15 percent feel mild itchiness. It can occur year-round, but is more frequent in the spring. Notably, in 69 percent of cases the rash is preceded by a simple upper respiratory infection.
Thought to be caused by reactivation of herpes viruses 6 and 7- which causes roseola in infants – the rash is usually the lone symptom, but some patients get a low-grade temp, headache, fatigue and nausea.
The rash is so typical it is usually diagnosed with a glance, but could be occasionally confused with Lyme disease, ringworm or psoriasis. It lasts three to 12 weeks and can be helped with the antiviral Acyclovir. Sunlight helps it heal, and moisturizers and antihistamines can be used by people who itch.