Pityriasis is a flat skin rash, occurring under the skin, which is common in older children and young adults. The pityriasis rash begins as a single oval shaped mark, sometimes called the herald, which is often missed or is misdiagnosed as ringworm. Additional marks begin to form under the skin, usually affecting the trunk and lower body, though marks can appear on any part of the body.

Though pityriasis causes an unsightly rash, it is not thought dangerous. Presence of a rash that lasts for more than a few days should mean a visit to a physician when possible, to rule out other more serious causes of rashes. Pityriasis is generally not uncomfortable or itchy, as the skin is not raised or irritated. However, the rash can be annoying because it can last for up to three months.

There are two forms of pityriasis: rosea, described above, and pityriasis lichenoides. Lichenoides can cause scaling, even though its formation resembles rosea. It also suggests one may have an autoimmune disorder. Those diagnosed with lichenoides will probably need follow-up care and testing to rule out HIV, mononucleosis, and certain forms of Hepatitis as these can be causal factors.

Both forms of pityriasis can occur without any underlying symptoms and are thought to be of viral origin. Neither form is particularly contagious, though occasionally in families one will see more than one person with pityriasis. This is probably a result of exposure to the same viral cause.

Though itching is uncommon with pityriasis rosea, it may be present in the lichenoides form. Treatments proposed are similar to treatments for rashes such as those received from contact with poison oak or ivy. Oatmeal baths and calamine lotion may be helpful. Antihistamines may also reduce itching and promote better sleep at night.

Pityriasis usually resolves by itself and requires no treatment. However, where autoimmune conditions or other viruses have been detected as precursors to pityriasis lichenoides, various treatments may be employed to address these conditions.

Some suggest sun exposure may help reduce the length of time one suffers from a pityriasis rash. Sun exposure may also cause the rash to worsen, as the skin may be hypersensitive. Additional damage to the skin may occur through sunburn.

The milder form, pityriasis rosea, is in most cases simply an annoying and unattractive rash which must be given time to improve. Should the condition not improve within the time frame given to one by a physician, it is advisable to contact the physician again for further instructions or advice.