When a patient with lupus erythematosus sees a doctor, the doctor often asks: Has there been any rash or redness on the face or body? Has the rash worsened after sun exposure? So why do doctors pay special attention to the sun exposure of SLE patients? It is because when SLE patients are exposed to the sun, the ultraviolet radiation from the sun will not only aggravate the rash on the face or other parts of the body, but also aggravate the symptoms of the whole body, which is called “photoallergy” in medical science. Photoallergy is an important feature of lupus erythematosus and an important reason for the onset or aggravation of lupus erythematosus. Why are lupus patients particularly allergic to sunlight? The ultraviolet rays in the sun have a damaging effect on the cells in our skin, which can cause damage to the cells in the skin. In normal people, these damaged cells are quickly removed by a type of cell (called macrophage) in our body that is responsible for cleaning, and new cells are quickly grown, so normal people can have peeling skin after strong sunlight, but no rash, erythema, or other symptoms of lupus. However, the macrophages of lupus patients are impaired and their ability to clean the skin is weakened, so when the patient is exposed to sunlight, the damaged cells in the skin cells cannot be removed in time, so these cells become “necrotic”, and the “necrotic” cells release a lot of “necrosis”. The “necrotic” cells release a lot of “bad molecules” that can inflame the blood vessels of the skin, thus aggravating the rash or causing a new rash to appear. At the same time, the necrotic cells also increase the activity of the immune system in our body, which then produces a series of reactions and finally produces some “bad” things to destroy our own cells, making the systemic symptoms of lupus patients worse. Therefore, for patients with lupus erythematosus, sun exposure should be strictly prohibited, and they should do a good job of protection in general, such as wearing broad-brimmed hats, long-sleeved shirts and sunglasses, etc. They should be fully prepared for travel, and even on cloudy days, they should also do a good job of UV protection, so that they can live a healthy and happy life.