In many cases, a doctor will be able to make a diagnosis by simply looking at the skin. When it isn’t clear what is causing the symptoms, additional tests may be necessary. For instance, the doctor may perform phototesting—a procedure in which the professional exposes a small area of the skin to certain amounts of ultraviolet light to confirm whether or not the skin eruptions are sun-related. The doctor may also order blood tests to rule out other conditions such as lupus.

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