Short-term sun damage presents as a sunburn. Long-term, unprotected exposure causes gradual damage to skin known as sun damage or photoaging, and accounts for about 90% of the signs of skin aging. The two main types of damaging rays are UVB and UVA. They damage skin cells and their DNA, leading to fine lines, wrinkles, irregular pigmentation, visible vessels, thinned skin, loss of elasticity and skin cancer (including melanoma). This damage occurs directly by the incoming UV photons and indirectly by free radicals that are generated by these rays.
UVA rays (320-400nm) can pass through glass and clouds and are present every day of the year at equal intensity during all daylight hours. They account for 95% of UV rays that reach the earth. Since UVA rays are longer in wavelength than UVB, they are able to penetrate into the deeper skin layers (dermis) affecting collagen, elastin and blood vessels. UVA plays a major role in photoaging. It can also damage skin cells in the basal layer of the epidermis where most skin cancers arise (e.g. basal cell and squamous cell carcinoma). UVA light is used in tanning booths, causing the same skin and eye damage as natural sunlight.
UVB rays (290-320nm) are the main cause of tan and sunburn because they damage the skin’s more superficial epidermal layers. UVB rays play a big part in the development of skin cancer, and a contributory role in photoaging and tanning. UVB rays account for 5% of the sun’s rays and vary according to season and weather conditions; they are more intense in the summer and at high altitudes. Over the last 25 years, more UVB rays have been penetrating the atmosphere because of the thinning ozone layer, increasing the risk for UBV-related sun damage. The SPF number shows the level of protection from UVB rays.
More focus has been placed on IR rays in the last few years. These rays are absorbed by the skin, converted into heat and contribute to photoaging along with UVA and UVB.
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