Early studies from the 1960s suggested that UVB was most important in causing photosensitivity in lupus. More recent research shows that UVA is also partly responsible.
How the UV rays ffect the skin is uncertain; probably, skin cell proteins and genetic material such as DNA and RNA start a reaction in genetically predisposed individuals. This relationship is explained further below.
How does a lupus rash develop after sun exposure?
A current theory, based on experimental evidence, is that UV light causes skin cells to express particular proteins on their surface. These proteins, including one called "Ro," may then be the targets of antibodies which latch on to them. The attached antibodies are thought to attract white blood cells which attack the skin cells, leading to the inflammation that causes the rash.
Normally, skin (and other) cells that are sufficiently damaged die through a process known as programmed cell death, or "apoptosis." The body then gets rid of the dead cells. But in lupus, apoptosis in the skin seems to occur more often than it should, which may in turn lead to more inflammation.
Another contributor to the lupus rash may be that too much of the inflammation-promoting substancenitric oxideis made in lupus skin after sun exposure. This then leads to further redness and inflammation.
The reasons for these abnormal reactions (beyond a genetic tendency to them) are unknown, but many potentially exciting research studies are ongoing in this field.
What do the different lupus rashes look like?
1) Acute cutaneous lupus erythematosus (ACLE):
- This is also known as the "butterfly rash" of lupus and occurs over the cheeks and nose.
- It often comes on after sun exposure, and is associated with lupus flares.
- ACLE usually heals within weeks without scarring.