ABSTRACT
Skin disorders may be generalized, localized to one or several sites of abnormality known as ‘lesions’, or eruptive, in which case many lesions appear spottily over the skin. The degree of erythema depends on the degree of oxygenation of the blood, its rate of flow and the site, and the number and size of the skin’s blood vessels. Different disorders tend to be associated with particular shades of red due to characteristic alterations to the blood vessels and surrounding tissues. Psoriatic plaques, for example, tend to be dark red in colour rather than pink, bright red or bluish red. Measurement of the degree of erythema may be helpful in assessing the effects of treatment on an erythematous skin disease. There are two types of device that can be used to do this; one is based on the comparator principle and the other uses reflectance spectroscopy. Both employ complex electronics, are available commercially and are easy to use.
