The sunscreen market is complex, competitive and confusing to consumers and healthcare providers alike. Because dermatologic patients look to their providers for expert advice about sun protection, it behooves us to offer accurate information and practical guidelines for obtaining the best products, especially because many of the private label offerings many dermatologists dispense in their offices are inferior in their efficacy.
UV Radiation, simplified
The majority of ultraviolet radiation (UV) reaching the surface of the earth is UVA (320-400nm), which consists of UVA2 (320–340nm) and UVA1 (340–400nm). UVA, which penetrates most deeply into the skin, is widely believed to be the primary cause of photoaging, including melasma and other dyschromias. It also causes the immediate pigment darkening seen during and immediately after sun exposure and are the predominant rays used in tanning booths. UVA also suppresses the immune system and has been shown to be correlated with the development of melanoma.1
UVB (290–320 nm), with its increased risk of sunburn compared to UVA, is associated with the delayed tanning that peaks about 3 days after sun exposure, usually after a sunburn, and appears to contribute to the development of actinic keratoses and skin cancers such as squamous cell carcinoma, basal cell carcinoma, and melanoma.2
While UVC (200–290nm), with the highest energy of the ultraviolet spectrum, would theoretically carry the highest risk of sunburn, it penetrates the least into skin and is mostly absorbed by the ozone layer, so this is not a big concern.
Visible light, encompassing wavelengths from 380–740nm, is frequently overlooked as a significant contributor to dyspigmentation, and should be a consideration for patients with this issue.
Infrared light (heat) includes longer wavelengths than visible light, from 700nm to 1mm.2,3 Some studies show infrared can have beneficial effects on skin texture and wrinkles by stimulating fibroblasts to produce collagen and elastin.4 Light-emitting diodes (LED) produce light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum and have been found to have some photomodulatory effects on the skin.5
How should we explain SPF to our patients?
One of the biggest hurdles to making informed choices in sunscreen selection is correcting misconceptions about what SPF actually stands for. SPF, or sun protective factor, is a relative measure of how long a product protects one from UVB only; it makes no reference to protection from other light wavelengths. This in part explains why patients who use high SPF products don’t burn, but do tan; they are often inadequately protected from UVA. Products with high SPF does not lead to protection from deeper-penetrating wavelengths such as UVA. To add to the confusion, in the US, sunscreens containing only a modicum of UVA protection are permitted to be categorized as broad-spectrum. Unfortunately, given the lack of significant UVA protection in these “broad spectrum” sunscreens, fair-skinned individuals using such products for a few hours at the beach may protect themselves from UVB (and thus sunburn) but could get as much UVA exposure as if they had done several sessions at a tanning salon.6
Many sunscreens manufactured outside the US include a secondary notation system for persistent pigment darkening (PPD) in addition to SPF. The key difference between the two systems is that PPD pertains to UVA, while as previously mentioned, SPF refers to UVB. Furthermore, a new category of UVA protection called PA (Protection Grade of UVA) has simplified the older PPD scheme by rating products with the use of plus signs—the more plus signs present, the more UVA protection afforded. The use of PPD and PA scoring, combined with SPF, will allow more intelligent choices in sun protection.
What is the difference between sunscreen and sunblock?
Another key distinction is that between sunscreens and sunblocks, given that “sunscreen” has become a colloquialism for any sun protective product. Sunscreen refers to chemical sun protectants that absorb UV photons, while sunblock refers to physical blockers that actually scatter UV photons.
What are the commonly used ingredients in chemical sunscreens in the US?
The primary chemicals used in American sunscreens to protect against UVB by means of absorption include cinnamates, salicylates, benzophenones (including oxybenzone and dioxybenzone), octocrylene, ensulizole, and camphor derivatives. (Use of aminobenzoates, the most potent UVB absorbers, has almost entirely disappeared as the FDA has shown that aminobenzoic acid (PABA) and trolamine salicylate