�Ͼ�ҽ�ƴ�ѧ��һ�ٴ�ҽѧԺƤ���� �Ͼ�ҽ�ƴ�ѧ��һ����ҽԺƤ���Բ���

������ʱ�����µ���Ƥ�������Ի���Դ���ϻ����ı䣬���ɻ����������µĶ��������˻���Դ���ϻ�����֮���������ԵIJ�ͬ�����ߵĽ�����Ҫ���չ��е����������鵼���ʳ�Ϊ���ϻ�������������ø��ϸ�����������������Ų��ݺ��ӵ����ã���ϸ�����ϻ�������ء�Ƥ����Դ���ϻ���Ҫ��ϸ�������н����ԵĶ����������£����ڹⱩ¶��Ƥ������Դ���ϻ��Ľ��̱������������Ŵ�

Human skin provides an instructive contrast between programmed or intrinsic aging, which is attributable to the passage of time alone, and superimposed additional changes or extrinsic aging that results from environmental damage. The latter process is mainly due to ultraviolet irradiation and is termed as photoaging. Telomere and telomerase exert essential roles in cell cycle, and closely associated with cell aging. The intrinsic aging primarily results from the progressive shortening of telomere, while the process is enlarged in sun-exposed skin by the environment.