Why Zinc?

Sunscreen Protection

There are two key facets of UV production that cause zinc to provide better protection than avobenzone. The first is UV spectrum coverage and the second is photostability. These two characteristics of sunscreen speak to how much UV protection is provided and for how long. The FDA monograph states that avobenzone can only be used at maximum concentration in any sunscreen at 3%. Zinc is safe enough to use at a maximum concentration of 25%.

UV Spectrum Coverage

The chart below is a comparison of UVA/UVB rays absorbed or reflected by these two ingredients. This chart is a measurement of UV protection as indicated by the space under each curve. For avobenzone at 3% (the blue curve), and Zinc (Zano, the red curve) at 7.5%. Note that all areas under the curves represent the portion of UV rays that are screened with specific wavelengths indicated along the X-axis.

The area under the Zinc curve (top/red) is greater than the area under the avobenzone curve (lower/blue), indicating Zinc Provides better UV protection for all UVA/UVB wavelengths. The data presented in this graph is from an evaluation after initial application and does not take into account the rapid erosion of effectiveness for avobenzone.

Photostability

Photostability, the second key sunscreen criteria after actual UVA/UVB protection, is a measurement of how long a specific sunscreen will protect. This is a key component to sunscreen comparisons due to the fact that many UV protective ingredients absorb rather than reflect UV rays. As rays are absorbed by a UV protective ingredient, the protection provided by that ingredient is eroded. Physical UV protectors such as Zinc and Titanium Dioxide do not substantially change their chemical composition when exposed to UV rays. Furthermore, avobenzone as a chemical is not inherently photo stable. It requires the addition of other chemicals to make it photostable. Without these additional chemicals Avobenzone erodes rapidly. The chart below shows a photostability erosion comparison of a 3% unstabilized avobenzone concentration, versus a 7% Zinc concentration. The UV protections of both concentrations was initially measured, and then each was exposed to the same amount of UV light equal to 4 MEDs (5.7 J/cm2 TUV per MED)_

UV protection remaining after 4 MEDs.

INGREDIENT	UVA	UVB
ZInc: 7% (Zano)	92%	91%
Avobenzone: 3%	51%	75%

Note that the UVA protection provided by avobenzone after UV exposure had eroded by almost half, whereas the protection of Zinc had only eroded 8%. Because MEDs are an expression of UVB protection, the more rapid erosion of protection from cancer causing rays (UVA) is largely undetectable, except when an evaluation such as this is performed.

To achieve higher levels of UV protection, some sunscreen formulas containing avobenzone must add other UV protectors. oxybenzone is a UV protectant ingredient used to bolster the UV protection of avobenzone formulas. Studies show that Oxybenzone is one of the least safe UV protectors because it is absorbed into the skin and can prove to be irritating to users with certain sensitivity. Among studies drawing that conclusion are:

A 2008 study (2) found oxybenzone present in 96.8% of 2,517 urine samples collected as part of the 2003-2004 National Health and Nutrition Examination Survey. This indicates that for about all users of avobenzone sunscreen with oxybenzone, a certain percentage of oxybenzone is absorbed into the body with daily application. All common sunscreens penetrated the stratum corneum but only oxybenzone is proved to present appreciable amounts in deeper tissue and the system.
A 2001 German study (3) found oxybenzone has also been detected in human breast milk following topical application. Women that are pregnant or breastfeeding, in particular, should be cautious and avoid sunscreen products containing oxybenzone. Initial research in both these studies (2-3) suggested that some form of toxicity might be present as a result of oxybenzone absorption. While no such analysis has yet been performed, products in the European Union intended for sun and skin protection containing 0.5% of oxybenzone are required to be labeled, "Contains oxybenzone."
Finally, photoallergic reactions to UV protectors are generally rare; a 2001 UK study (4) found oxybenzone to have a much higher rate of reactions compared with other UV protectors.

Sources:

1. Zano 10 and Xperse, excellent broad-band UV protection from mineral UV filters in personal care and sunscreen formulations, Measurements done in O/W emulsion to 4MEDs (5.7cm2 TUV per MED), McBride, pg 16, 7/26/2010.

2. Concentrations of Sunscreen Agent Benzophenone-3 in Residents of the United States: National Health and Nutrition Examination Survey 2003-2004, Antonio M. Calafat; Lee-Yang Wong; Xiaoyun Ye; John A. Reidy; Larry L. Needham, Posted: 08/11/2008; Environmental Health Perspectives. 2008; 116(7): 893-897. 2008 National Institute of Environmental Health Sciences.

3. Nachweis von UV-Filtersubstanzen in Muttermilch = Detection of sunscreen agents in human breast milk, Hany, J., Nagel, R., Henrich-Heine-Univ. Dusseldorf, medizinisches Inst. Umwelthyg., 40225 Dussldorf Allemagne.

4. Photoallergic contact dermatities is uncommon., Darvay A, White IR, Rycroft RJ, Jones AB, Hawk JL, McFadden JP., Department of Environmental Dermatology, St. John's Institute of Dermatology, St. Thomas' Hospital, Lambeth Palace Road, London SE1 7EH, UK.