Sunrays are composed of different types of energy.
Visible light energy probably has little effect on skin aging and the development of skin cancers.
Infrared (IR-A) rays may play a part, though not yet defined.
UVC rays, X-Rays, and several others do not reach the earth as they are absorbed by the atmosphere before reaching the ground.
The rays believed to be most harmful to the skin are UVB and UVA.
UVB (Burn) rays:
are absorbed by the atmosphere and significantly by the top layer of the skin,
are present mainly mid-day, in the summer, down South,
cause mainly sunburn by heating the top layer where most are absorbed (Many of the injured cells are sloughed and, therefore, do not cause permanent damage.)
Do not bounce,
Are minimally present indoors,
Makeup only 2 to 3% of the sunrays actually hitting us.
UVA (Aging) rays cause cellular damage leading to aging and skin cancer
They are present all day, all year, and at all latitudes,
They account for about 97-98% of the UV Rays hitting the skin.
They penetrate, not only the atmosphere, but also clothing, glass, and the skin.
In the skin, they cause direct tissue damage and the release of free oxygen radicals that further attack normal skin cells.
They are present on a cloudy day, in the car, in the house and anywhere with windows or fluorescent lights and even in the shade.
There is a lot of misinformation about the sun and sunscreens in spite of the fact we have had the proper information for over 20 years. Some things you need to know:
Products containing only UVB protection (indicated by SPF) keep us from getting sunburned, but allow us to stay in the sun longer, thus getting more UVA damage. (Even a high SPF does not protect from UVA.)
Many products are no longer allowed by the FDA to call themselves a “sunscreen” or “sunblock” but still put an SPF number on the label so you will think they can protect you. Unless they actually say sunscreen or sunblock, they are not protective even for a little while.
Assuming we do not need sun protection unless we are laying in it or out in the sun for an extended time also markedly increases our sun damage.
Most sunscreens need to be reapplied hourly if you are outdoors or near a window and every 2 hours otherwise. The only exception is zinc oxide, which remains present unless washed or rubbed off.
As of December, 2012, new FDA regulations required sunscreens to meet stricter requirements to be labeled “Broad Spectrum,” or to be called a “sunscreen” or “sunblock,” requiring the ability to block the full spectrum of UVB and UVA. The regulations, however, do not require any information on the effectiveness of the blockage. Some of the products that meet the new requirements do so for only a short while or incompletely, making them impractical since you must reapply them frequently as above to be protected. Instead, what we need to do is use one of the newer broad spectrum Sun Blocks containing clear Zinc Oxide (Z-Cote) daily. This goes on clear and is effective until washed or wiped off. We recommend reading the ingredients label looking only for Zinc Oxide or Z-Cote of at least 8%, and, preferably, 10% or more. This has the equivalent of an SPF of 20 to 50, and, thus, protects us from both UVA and UVB. Additionally, Vitamin-C Serum and SkinMedica Antioxidant Therapy are Topical Antioxidants. Their use prevents or reduces injury from any UVA rays that get through the sunblock and helps correct some previous damage.
Normal clothing does not block UVA. There are, however, many companies that now make sun protective clothing and Rit makes a product, SunGuard, that can wash sun protection into clothing for 20 washings (about 6 months).
Although we need some sun exposure to make Vitamin-D and some other chemicals that help keep us healthy and out blood pressure controlled, we do not as yet know how much is optimum to keep us healthy and not cause skin problems. Presently active people seem to balance this even with excellent sun protection.