Now that we've discussed what SPF is and how it's determined, we can get into a few of the ingredients that actually deliver the sun protection.
Octyl Methoxycinnamate (octinoxate) is the most common chemical sun blocking agent. It absorbs UVB rays and also has waterproofing qualities which makes it ideal for summertime fun. When exposed to the sun, Octyl Methoxycinnamate loses some of its effectiveness so it is rarely the single sun blocking ingredient found in a sunscreen formula.
Octyl Salicylate is a less effective UVB absorber. It is often used in conjunction with other blocking agents as its effectiveness decreases upon sun exposure. Although uncommon, this ingredient has been known to produce mild skin irritation. There is also concern that this ingredient is a penetration enhancer which means it may make the skin more susceptible to invasion by other topical treatments that ordinarily couldn’t pass through the skin’s natural barriers.
Oxybenzone and its close cousin Sulisobenzone are both photo stable (not affected by sunlight) chemical UVB absorbers. They are typically used to stabilize other UVB absorbers that degrade with sun exposure. These chemicals can possibly be absorbed by the skin and raise concern of free radical invasion.
Titanium Dioxide is a physical sun blocking agent that is effective in the UVB and UVA range of the light spectrum. It covers the full UVB range however it doesn’t reach the peak region of UVA. Titanium Dioxide is a common sun blocker in natural formulations. It is very efficient in preventing sunburn; however since it does not cover the entire UVA spectrum, skin cancer is still a relative concern. Most over the counter sunscreens that contain this ingredient incorporate other chemical and physical UV blockers.
Although Titanium Dioxide is stable, it has been known to cause reactions with other chemicals which again raises the possibility of free radical formation. This ingredient is unsightly as it goes on white and stays white. Titanium Dioxide nanoparticles (super small) are a more esthetically pleasing option because they leave a less noticeable white residue, but the verdict is still out on the safety of such. On a positive note, Titanium Dioxide is not known to cause skin irritation and is even safe to use on sensitive skin.
Zinc Oxide is another common physical sun blocker that is actually more effective and less reactive than Titanium Dioxide. In fact it covers the full range of UVB and UVA wavelengths which makes it the most effective single ingredient sunscreen available. Even so, it is usually used in conjunction with other chemical protectors. Zinc Oxide is not a known skin irritant and it can be used on sensitive skin. Similar to Titanium Dioxide, Zinc Oxide leaves a white residue on the skin. In nanoparticle form there is the threat of formation of free radicals, however, scientists have been successful in coating the nanoparticles to prevent such occurrences.
What's in your favorite sunscreen?