UV Damage – How does it happen;
This damage is done directly or indirectly. The Direct damage is through
absorption of energy, which is largely the energy of UV-B, which can kill cells.
Otherwise the damage occurs indirectly through intermediates such as certain
chemicals, which are photo-activators, or through the production of reactive
oxygen species. This seems to be the method of damage caused by UVA.
The DNA, the cell walls, or the structures within the cells may be damaged. Most
important is DNA damage, which can be detected as either strand breaks or as
changes to the chemicals, which form the complex DNA spiral. The most
common changes are 8-hydroxydeoxyguanosine (8OHdG) from UVA exposure
and cyclobutane pyrimidine dimers from UVB exposure. This may cause
incorrect messages to be sent from the DNA to the cell. Cells are protected by
free radical scavengers that may remove potentially mutagenic compounds.
There is an extensive repair capacity for removing
 strand breaks,
 small base modifications
 big chemical changes lesions (cyclobutane pyrimidine dimers).
UV also stimulates the cell to produce early response genes that activate a
cascade of repair mechanisms to facilitate repair processes prior to replication
and division. If the cell is not rescued then this will ultimately lead to the
development of abnormal cells, (and maybe cancer) or may cause cell death,
and apoptosis may be induced.
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