Let’s begin by clearing up the confusion regarding SPF. The acronym stands for Sun Protection Factor, but it’s a woefully inadequate descriptor. The term was coined by Franz Greiter in 1962 as a standard for measuring the effectiveness of sunscreen when uniformly applied at a rate of two milligram per square centimeter. That’s roughly equivalent to applying a shot-glass full of sunscreen to your entire body. The FDA adopted the term and subsequently required sunscreen manufacturers to provide SPF protection against UVB radiation. The problem is that UVB is only one form of damaging radiation.
Types of damaging radiation
Sunlight is a type of electromagnetic radiation (EMR). EMR covers the entire spectrum of energies released by stars including our sun. These energies travel in waves measured in atomic units known as nanometers. Below is an image of all known EMR and a scale showing their measurements in nanometers (nm). The EMR we need shield against is ultraviolet radiation or UVR and its place in the EMR spectrum is depicted below. It’s called “ultra” violet because it lies outside the range of visible light; i.e., we can’t see UVR like we can see daylight
The UVR wave-lengths we’re screening against range between 200 and 400 nm long. UVR measuring between 290 and 320 nm is named UVB and radiation measuring 320-400 nm is called UVA (Moore 2007).
UVR is dangerous because of its small size. The smaller the length of a ray of light, the more energy it contains. UVR is small and so energy packed that it causes molecules to split up. It actually knocks electrons out of their orbits destabilizing atoms and generating free radicals. Free radicals are those infamous progenitors of wrinkles, suns spots and skin cancer.
The energy contained in ultraviolet light causes molecular DNA to break apart, promoting photoaging and skin cancer.
FDA regulatory changes regarding SPF
When the FDA originally mandated sunscreen manufacturers to include an SPF rating, medical researchers were primarily concerned about UVB and its role in promoting skin cancer. However as early as 1978, the FDA acknowledged the skin damaging effects of UVA and opened inquiries into extending SPF labeling to include both UVA and UVB ratings. Finally in 2011, the FDA announced regulatory changes summarized below.
- Companies must indicate if they provide both UVA and UVB protection.
- If they do, they can label their products as “Broad Spectrum SPF.”
- Sunscreens may be labeled broad-spectrum if they provide “proportional” protection against both UVA and UVB. In other words, a product with an SPF of 15 must provide an SPF of 15 for both UVA and UVB.
- Manufacturers can label “water resistant” but the label must show whether it will last 40 or 80 minutes while sweating or being in water.
- It remains unclear, but it appears manufacturers may be required to cap their SPF ratings at 50 because there is very little addition sun protection after a rating of 30. The graph below makes the FDA’s point.
Interpretation of the graph
- SPF 15 blocks 93% of UVB rays
- SPF 30 blocks 97% of UVB rays
- SPF 50 blocks 98% of UVB rays
The difference between SPF 15 and SPF 30 is an increment of only four percent – provided of course you apply a layer that’s two milligrams thick. Most people under-apply and use ¼ to ½ the required amount. A half application of an SPF 30 provides and effective SPF of 5.5 (Autier 2000).
As can be expected, manufacturers are strongly resisting an SPF cap ruling because it would cut into profits. The NY York Times reports that Americans buy $680 million worth of sunscreen every year and the volume is growing.
TheFDA changes are scheduled to go into effect June 18, 2012 and small manufacturers selling less than $25,000 a year in product have one year to comply while larger companies have until June 2014.
Quick UVA and UVB facts
- UVB – 5% of all sunlight that reaches earth is UVB and is widely considered the key culprit behind skin cancer.
- UVA – 95% of all sunlight to reach earth is UVA and it penetrates deeply into the skin and is largely responsible for photoaging (Gruijl 2002).
- UVA light is responsible for the classic signs of photoaged skin including wrinkling, dryness, and loss of elasticity (Lowe 1995 and Lavker 1995).
UVA penetrates much deeper than UVB and accounts for 95% of all solar radiation that reaches the earth.