Skin cancer is a problem which can be caused by or made worse by sun exposure. Sunlight can cause immune damage. Based on scientific studies conducted by immunologists over the last several decades, we are being warned that while some sunlight is vital, too much can be very dangerous. While sunlight provides the body with essential vitamin D, it also has a negative effect on T cells.
T cells are that part of the immune system which turn an immune response on and off.
When the need for an immune response is over, a suppressor T cell turns the response off. Recent research has found sunlight can destroy helper T cells, causing a lowered immune response. A scenario which might be illustrative of the danger of sunlight is after a sunburn. The sunburn would be accompanied by a lowered helper T cell count and an elevated suppressor T cell count. Arthur and Loretta Balin in their book, The Life of the Skin.