SunScreens and Sun Damage

Photoaging as opposed to normal temporal aging is due to exposure to the sun’s radiation. These rays, UVA/UVB, (280-400nml on the spectrum) are from the ultraviolet portion of the light spectrum,

UVB(short length) rays penetrate just into the epidermis,were once thought to be the culprits in the affect on the epidermis, but UVA(long length) rays which penetrate deeply (through the body)are now known to be equally if not more damaging. Many lines of evidence indicate that the primary biological actions of UVA radiation involve DNA damage.

UVB emissions from the sun undergo significant seasonal variations; the UVA emissions, however, do not appreciably change over the course of the year. The amount of solar UVA reaching the earth's surface is much greater than that of UVB. Also, UVA is transmitted by most window glass and many plastics that do not transmit UVB.

Photoaging of your skin with fine lines, wrinkles, dilated pores, laxity and sagging of skin are the direct result of sun damage to the underlying collagen and elastin fibers. Sallow complexion due to increase in epithelial area. Hyperpigmentation can be caused or exacerbated by the sun’s stimulation of the melanocytes, causing over-production of melanin resulting in “freckles, lentigoes, and poikiloderma of civatte (reddish hyperpigmented area with telanctasias on the neck). Telangectasias(“broken blood vessels”)are also increased due to the damage to the skin’s vasculature. Finally formation of pre-cancerous and cancerous lesions after prolonged damage to the skin cell DNA.

Sunscreens use a variety of ingredients to protect your skin. There are chemicals that “absorb” the rays and there are physical blockers ( titantium dioxide, zinc oxide, iron oxide)> As to SPF ratings , they only apply to UVB as UVA protection cannot be measured as the chemicals are destroyed by the rays and the air. Thus the need for broad spectrum coverage. So make sure your sunscreen protects from both UVB and UVA.
As to the amount of protection needed:

SPF Rating Amount Blocked
SPF 2 50%
SPF 4 75%
SPF 10 90%
SPF 30 96.67%
SPF 50 98%
SPF 70 98.57
SPF 100 99%

As you see no sunscreen product screens out all UV rays. So use a good broad spectrum as directed and try to minimize your exposure between the hours of 10 a.m. and 3 p.m. As to infrared rays which we feel as “warmth” their effects are not known at this time .