Abnormal light sensitivity, or "photosensitivity," is a major feature of both systemic lupus erythematosus (SLE), which can affect any organ or system of the body, and cutaneous lupus, which is mainly limited to the skin.
The two most common forms of cutaneous lupus are discoid lupus erythematosus (DLE) and subacute cutaneous lupus erythematosus (SCLE). DLE and SCLE are described in detail below.
How common is photosensitivity in lupus?
The American College of Rheumatology loosely defines photosensitivity as "a skin rash as a result of unusual reaction to sunlight." Using this definition, photosensitivity has been identified in one-half to three-fourths of people with systemic lupus.
In people with cutaneous lupus, photosensitivity affects 50 percent of those with discoid lupus and 70-90 percent of those with subacute cutaneous lupus.
How does photosensitivity show up in lupus?
- Sunlight can cause new skin lupus lesions (sores).
- Flares of internal lupus disease, including joint pains and fatigue, can also be triggered by sunlight.
- Some medications increase the effects of the sun on a person's body. People with lupus taking these drugsincluding tetracycline antibiotics and many othersmay also very occasionally develop "phototoxic" reactions. These will lead to easy sunburning, so if you are taking these "photosensitizing" medications, you will need extra protection against sunlight. Ask your doctor or pharmacist if any of your current or new medications might make you extra-sensitive to the sun.
Why are people with lupus so photosensitive?
The science of sunlight in lupus is complex and poorly understood.
- Several studies over the last 30 years have looked at the role of ultraviolet (UV) light in lupus.
- UV light is invisible radiation from the sun. It has a shorter wavelength than the visible light and heat we all recognize.
- UV is divided into UVA, UVB and UVC (which does not reach us because it is absorbed by the atmosphere).
- In general, UVA mostly ages the skin and UVB mostly burns the skin ("A Ages, B Burns") although UVB also contributes considerably to skin aging and cancer.