photoaging

photoaging

Photoaging is caused by the damaged DNA by UV light. The reaction of the inside skin is to release nitrous oxide to induce the production of melanin. Then the horny layer is thickened, and this may make the surface of the skin feel rough. The influences include epidermis (keratinocytes, melanocytes, and Langerhans cells), dermis (fibroblasts, collagen and elastin), blood vessels, and water-retaining substances between the cells. 

UV irradiation promotes the release of active substances which will cause the keratinocytes and keratinocyte stem cells may produce clones of abnormal cells. They are varying size, pycnotic nuclei with abnormal DNA, and an irregular growth pattern. They will leads to an impaired barrier (stratum corneum) and, subsequently, dry skin. The appearance will be thickened with rough skin.
Langerhans cells are in charge of immune functions. Irradiated Langerhans cells have fewer Birbeck granules and lose their dendritesThe above phenomena will progress into skin cancer, skin allergies, and prone to skin infections. 

Manifestation of wrinkles is due to fibroblasts produce less matrix substances of the dermis. One of the reasons is the loss of the anchoring fibrils below the basement membrane are destroyed by matrix metalloproteinase. Otherwise, collagen of the dermis is also destroyed by light. Collagen mRNA will be down-regulated, and with increased metalloproteinases.

The elastin fibers become thickened instead of forming a healthy fine mesh to support the skin. Elastin fibers are fractured by UV light, and they roll up into little balls, especially on the neck skin. The skin starts to sag as the defective action of elastin and diminished support from collagen.
The skin becomes dry are also because of the less glycosaminoglycans and other water-retaining molecules in the skin. UV light could also damage the collagen support around blood vessels which causes dilation of these vessels for poor circulation.

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