 SU may be classified based on the wavelength of the radiative energy that causes the allergic reaction; known as Harber's classification, six types have been identified in this system.Type I solar urticaria is caused by UVB (ultraviolet B) radiation, with wavelengths ranging from 290–320 nm.Type II is induced by UVA (ultraviolet A) radiation with wavelengths that can range from 320–400 nm.