Before we talk about uva testing, let’s examine why we think uva protection is important and how that relates to sunscreen use.
UVA rays penetrate deeper into the skin layer than UVB rays. Excess exposure to UVA rays may cause premature skin aging, wrinkling, and cell damage and to a lesser degree than UVB rays, damage to the epidermis (redness and sunburn). However, there are many other factors that cause cell damage. With respect to premature aging, other risks beside sun overexposure are diet, smoking, environmental pollutants, stress, and lack of sleep. Likewise, factors such as family history and genetics, skin type, and weakened immune system also contribute to skin cancer. Getting sunburned does damage the skin and increase your risk for both skin cancer and photo-aging. Sunscreen does prevent sunburn. But sunscreen use alone does not help prevent the effects of cell damage.
Even the FDA finds that there are not enough data to support these claims – “FDA has tentatively concluded that the available evidence fails to show that sunscreen use alone helps prevent skin cancer or premature skin aging. Thus, the antiaging, skin cancer, and sun damage claims…would be false or misleading due to lack of sufficient data in support of these claims.” However, sunscreen use as part of a comprehensive sun protection program that includes limiting sun exposure and wearing protective clothing for example will reduce your risk of cellular damage. To address these issues, the FDA is proposing a required “sun alert” statement in the Warnings section of the label to read something like this: ‘UV exposure from the sun increases the risk of skin cancer, premature skin aging, and other skin damage. It is important to decrease UV exposure by limiting time in the sun, wearing protective clothing, and using a sunscreen.’
There are just as many variances and discord with UVA testing as there are with UVB testing. Currently, there is no consensus on the best method for UVA testing. Three methods are being considered: the Persistent Pigment Darkening (PPD) test, the Protection Factor in UVA (PFA) test, and the Critical Wavelength test. Both the PPD and PFA are in vivo methods performed on live organisms. They are similar to the SPF testing in that they are based on erythema and pigment color changes. In the Critical Wavelength test, a 1 mg/cm2 thin film of the sunscreen is exposed to UV substrate spectrophotometry. It is an in vitro method of determining the critical wavelength where 90% absorption occurs over the integral from 290 to 400 nm.
UVA protection assessment, in vivo or in vitro, is beyond the scope of a home based analysis. However, existing UVA testing and research of commercially prepared sunscreen and zinc oxide manufacturers can serve as a benchmark. For micronized zinc oxide, BASF which manufactures Z-Cote® and Kobo Products Inc both show that even just 5% of their various grades of micronized ZnO give UVB and UVA coverage up to 380 nm.
To my knowledge, there are no current analysis of conventional zinc oxide as a sunscreen as it is not currently marketed as such. But that does not mean it is not an effective UVA/UVB protector. Back when zinc oxide was more popular, sunscreen was used to prevent sunburn, not provide UVA protection. Conventional zinc oxide does block some UVA rays but exactly how much I do not know. However, its protection is relative straightforward: the more opaque and higher the concentration, the more UV protection.
Update! Proof that regular zinc oxide blocks UVB/UVA rays
Not having uva testing data with conventional zinc oxide is not a concern to me. As I explained earlier, limiting UVA exposure is just one of many ways to reduce the risk of cellular damage. To combat premature aging and skin cancer, you are better off leading a healthy lifestyle that includes, for example, eating natural foods high in antioxidants.
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