04.14.08

How UVA Rays Age Skin

Posted in Facts About UV Protection, Skin Aging Facts at 10:34 pm by Administrator

The Future of Sun Protection

Sun protection has become a more complicated affair than simply smearing on the stuff made famous by a pig-tailed little girl. In fact, our then-adorable beach baby could probably be a poster model today, only now her leathery, wrinkled skin dotted with precancerous lesions would serve as a warning to us all of the long-term effects of too much sun-time. Being tan used to equate with being healthy, but this perception is gradually changing as we learn more about the long term effects of too much sun exposure. Especially for those who are interested in preserving our skins against the ravages of time any outdoor activity isn’t the same care-free pleasure it used to be. An overview of that day at the beach from the perspective of UV exposure will help us understand just why this is so.

Ultra Violet Light

The sun emits light at all different wavelengths in the electromagnetic spectrum, but the UV (ultraviolet) range is responsible for skin changes and aging.
Though some ultraviolet waves from the sun penetrate earth’s atmosphere, most of them, especially the short-length UVC rays, are blocked from entering by various gases like ozone. UV penetration fluctuates on a daily basis, with more ultraviolet waves getting through our atmosphere on some days than others. However, as the ozone layer thins we can count on more frequent and prolonged penetration of UVC rays.

The graph below describes the range we are talking about.
UV light
UVC—————-UVB———–UVA——-visible light
_________________________________________________
200-290 nm 290-320 nm 320-400nm 400-700nm

short waves/high energy <-------------> long waves/low energy
nm=nanometers (1 nanometer = 1 billionth of a meter)

The ABC’s of UV

UV C rays are the shortest, highest energy ultra violet light and are the closest to x rays on the scale (moving left). These are sterilizing rays that kill small organisms and are the most carcinogenic. Sunscreens provide no protection.
UV B rays are the burning rays, which penetrate to the epidermis and are present from 10 AM to 4PM. They are 1000 times stronger than UVA, stimulate melanin biosynthesis, and are linked to squamous cell carcinomas. They cause all the nasty symptoms of sunburn; edema, redness, and itching. They can also contribute to cataracts.

UVA, the long wave, low energy waves, are present from sunrise to sunset, enter the dermis and are 1000 times more prevalent than UVB rays. For low-energy waves they have a long list of inimical effects: they cross-link collagen and elastin, damage DNA, destroy langerhans cells and immune function, turn melanin darker and cause hyper, hypo-pigmentation and broken capillaries.

A good mnemonic is UVA = aging, UVB = burning and UVC = carcinoma

Aging Rays

Up until the present, more attention has been paid to the shorter wave-lengths, the UVB rays which measure from 290 to 320 nm. The reason for this is simply because their effects are rapidly obvious. When we are over-exposed we burn. Most sunscreens on the market concern themselves with protection in this range, and in fact, an SPF rating is an indication of how much protection you are getting, over a duration of time, from the burning rays. So an SPF rating of 2 would indicate that, if you can stay out in the sun for ten minutes without burning, you would be able to stay out for 20 minutes without burning wearing your SPF 2 protection. The testing for SPF is simply a matter of measuring duration of non-burning time on human skin, where the parameters are known.

This is a relatively easy test to perform, and one can understand why FDA requirements vis a vis testing are only concerned with UVB protection. However, an aging population has begun to pay attention to the UVA part of the spectrum, and for an overwhelmingly obvious reason. The UVA rays are the aging rays, responsible for hyperpigmentation, sun spots, redness and (shudder) wrinkles. UVA rays are different from UVB rays in other ways—they penetrate to the dermis rather than the epidermis where they may do longer-lasting damage, they are present from sun-up to sun-down and they go through clouds and glass. Because their effects are insidious damage testing is not as easy as it is with UVB–with UVA one doesn’t burn, one ages.

Unfortunately it is not safe to make the assumption that because one is wearing a sunscreen with a high SPF rating one is automatically protected against UVA rays. Remember, an SPF rating refers only to the UVB range. Indeed, the typical sunscreen which contains the most commonly used chemicals does NOT protect against UVA rays. For example, benzophenone -3 protects from 290-360 nm, while octyl methoxycinnimate protects in the 290 to 320 range.

Three ingredients commonly used by sunscreen manufacturers provide protection for the longer UV wave-lengths: Avobenzone, 310-400 nm, Titanium dioxide, 290 to 360 nm, and Zinc oxide, 290-400 nm. Avobenzone looks like a good bet, but unfortunately it degrades after 30 minutes in the sun, so sunscreens including avobenzone as an active ingredient must be applied very frequently if one is to receive adequate protection.

Range of Protection of Common Sun Protective Agents

UVC UVB UVA
200nm—–290nm——- 320nm—————-400nm _________________________________________________
200 245 290 300 310 320 330340350360370380390

PABA ————————–
Avobenzone (Parsol 178) ———————–
————Octyl methoxycinnimate
Octyl salicylate————
Oxybenzone————————————-
(Benzophenone-3)
Zinc oxide —————————————
Titanium dioxide —————————-

This leaves zinc oxide, an excellent choice as it is inert, anti-inflammatory and provides superior, full-spectrum protection. However, it has not been popular with the public as it tends to leave a white, greasy film on the skin. Since UVA protection is an everyday affair (this means EVERY day, not just when it’s sunny, but even on those cloudy days when you don’t plan on going outside) sunscreen formulation has become more and more the purlieu of the cosmetic chemist, who is faced with the challenge of formulating a product that is both protective and light enough for people to wear.

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