Urtica – colloquially called wheal or nettle – (pl. urticae; ICD-10 R21: skin rash and other nonspecific skin eruptions) refers in dermatology to a transient, circumscribed edema (water retention) in the upper cutis. The cutis is divided into the epidermis, a multilayered keratinized squamous epithelium, and the corium, a tight connective tissue rich in fibers.
The wheals can be the size of a pinhead to a coin, appear pale to bright red, occur singly or merge into larger areas. They represent a hemispherical or squamous, transient (<12 h) elevation.
If many wheals form an exanthema (extensive rash), it is called urticaria.
Urtica belongs to the so-called primary florescences. These are skin changes that are the direct result of a disease.
Urtica can be a symptom of many diseases (see under “Differential diagnoses”).
Course and prognosis: The course and prognosis depend on the cause. For example, if the wheals are allergic, they disappear spontaneously (on their own) as soon as the allergen as a trigger is eliminated. A wheal usually does not persist for long.
