Ultraviolet Radiation and the Limits to SPF (Sun Protection Factor)

Ultraviolet Rays in the Electromagnetic Wave spectrum

-The sun emits a wide spectrum of electromagnetic wavelengths, ranging from 100nm to 1mm, and classified into different spectral regions as ultraviolet (UV), visible and infrared radiation.
-UV radiation normally reaching the earth is a combination of Ultraviolet B (UVB) and UVA wavelengths.
-Excessive expossure of sun to UV radiation induces adverse effects, such as erythema (or sunburn reaction; mostly UVB), photoaging (mostly UVB), photoimmunosuppression (mostly UVA) and photocarginogenesis (UVA and UVB).

The Effects of Ultraviolet Radiation on the Skin and History of Sunscreens

-For many years, the focus of photobiology, research and photoprotection strategies has centred on the UV portion of the solar spectrum.
-The first sunscreens, commercialized in the beginning of the 20th century, were directed predominantly towards UVB, which is responsible for the most obvious effect, sunburn, and more delayed effects such as photoaging (along with suggested infrared light in 1982), precancerous conditions (actinic keratosis) and skin cancers (mainly non melanoma skin cancers (NMSC): Basal Cell Carcinoma and Squamous Cell Carcinoma).
–Newer sunscreens target UVAs as well which by the way penetrate the deeper dermis and subcutaneous layer and play a more important in the development of skin Cancers (mainly melanoma)

-Within the last decade, studies have inferred that wavelengths beyond the UV spectrum, in particular visible light and infrared radiation, contribute to skin damage.
-As a consequence, attempts have been made to develop sunscreens that not only protect against UVB and UVA radiation, but provide photoprotection against visible light and infrared radiation as well.

SPF and its Limitations

-The sun protection factor (SPF) has widely been used to evaluate the protective value of sunscreens. However, SPF only reflects the effectiveness of the sunscreen to protect against acute sunburn which is mainly due to UVB radiation. Increasing evidence points to deleterious effects of chronic UVA exposure. Therefore, broad spectrum photoprotection covering both the UVA and UVB range is desirable, and choosing sunscreen products simply basing on the SPF value will not be adequate.

-SPF is determined using a prescribed sunscreen application thickness of 2 mg/cm2. Therefore users should apply at least this quantity  of sunscreen  to obtain the level of UV protection expected from a product. In most cass, however, user apply insufficient amounts of sunscreen.

To read more about Sun protection Factor “inflation” (SPF), click here

What are the future Sunscreens ?

A new trend has emerged of adding antioxydants into commercial sunscreen preparations in order to reduce the photo-oxidative damage that results from UV-induced reactive oxygen species production, providing a sort of non-sunscreen photoprotection and supplement the photoprotective effects of sunscreens.

Remarks
-there is NO known infrared filter ! (pigments in sunblock (tinted sunscreens) can scatter radiation but no studies exist as to how effective this is)
-No tinted sunscreens claim that they protect against visible light or infrared rays

Source of information: Tian E – Throwing light on photoprotection – Beyond SPF. Symposium 5 – The Dark Side of Light – Effects of Light on Skin, and Photoprotection NSC Update in Dermatology and Venereology 2015 – Singapore