Why are lupus patients sensitive to sunlight?
The science of sunlight in lupus is complex and poorly understood. Several studies over the last 30 years have examined the role of ultraviolet light in lupus. Ultraviolet light (UV) is invisible light from the sun with a shorter wavelength than visible light. Ultraviolet light is divided into UVA, UVB and UVC (which does not reach us because it is absorbed into the atmosphere). In general, UVA ages the skin and the UVB burns (ie A ages, B burns). Early studies from the 1960s suggested that only UVB was important in causing photosensitivity in lupus. However, more recent studies have shown than UVA can also cause skin problems in lupus. The substances in the skin that react with the UV light in lupus are unknown but the suspects include various proteins, as well as genetic material (“DNA” and “RNA”). How does my rash develop after sun exposure? The current theory, based on experimental evidence, is that UV light causes skin cells to express particular protein molecules (“antigens”) on
