UV Rays and the Skin Cancer process

The most dangerous part of sunlight is the waves in the high-energy ultraviolet (UV) region. These come in three types, ranging from low to high energy: UV-A, UV-B, and UV-C.

UV-A rays penetrate deepest into the skin.  While it is unclear how many skin cancers are attributable to UV-A, they are not blocked by glass.

UV-B causes most sunburns and experts think, most skin cancer.l  Some UV-B is partly absorbed by high-altitude ozone.  It is blocked by window glass, most sunglasses, and to varying degrees) sunblocks.  A few insidious rays, however, penetrate the top layer of the skin and cause aging, immune-system damage and cancer.

UV-C are entirely absorbed by ozone molecules in the atmosphere.

As you can see, most of the concern focuses on UV-B.  These rays penetrate the epidermis (the top layer) and damage skin cells.  If UV-B passes through a cell nucleus, it can strike DNA molecules in the chromosomes, breaking them or forming abnormal chemical bonds.

In severe cases, entire chromosomes can be reshuffled.  Sunlight is most damaging in childhood, when cells are dividing rapidly, thereby creating opportunities for persistent mutations.  Once the cell's DNA mutations have occured the chances of melanoma tumors developing is notably increased.  This is what we understand currently about the UV link to DNA and melanoma.  Continuing research is being undertaken on the ability of UV-B radiation to damage the cell's chromosomes.  Previous studies at M. D. Anderson have shown that melanoma patients often have a reduced capacity to repair the DNA damage from UV-B exposure.  For further information please go to www.mdanderson.org/diseases/melanoma/