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Does sunscreen damage skin?

Higher-energy UVB rays are the primary cause of sunburn, and bind directly to DNA causing pre-cancerous mutations. However, the sun’s more numerous lower-energy UVA rays penetrate deeper into skin tissue and are most responsible for generating free radicals that may damage DNA and skin cells (Marrot 2005), promote skin aging (Wlasckek 2001), and cause skin cancer (Wittgen 2007).

Sunscreens can help reduce UV-related free radical damage by diverting the radiation from the skin, but the ingredients themselves can release their own free radicals in the process. When the sunscreen molecules absorb UV energy, diverting it from the skin, the molecules dispel this excess energy by releasing free radicals. In a delicate balancing act, an effective sunscreen prevents more free radical damage (from UV radiation) than it creates through its own free radical generation. It reduces UV exposure without itself damaging skin. Sunscreen makers commonly add antioxidants to their products to soak up free radicals from either source, UV radiation or sunscreen itself.

Most of the US-approved UV filters release free radicals – octylmethoxycinnamate, oxybenzone, Avobenzone, octocrylene, titanium dioxide, zinc oxide, Padimate O, PABA, menthyl anthranilate, and Mexoryl SX (Allen 1996, Beeby 2000, Cantrell 1999, Damiani 2007 & 2010, Dondi 2006, Hidaka 2006, Knowland 1993, Sayre 2005, Serpone 2002). Some benzophenones, octisalate, and Mexoryl appear to produce no free radicals (Allen 1996, Fourtanier 2008).

Sunscreens typically do more good than harm in this regard (Popov 2009, Serpone 2006, Haywood 2003). But they could be better. Tests show that sunscreen generally diminishes the formation of these free radicals—one study indicates a 45% reduction at typical amounts and a 55% reduction at the 2 mg/cm2 recommended use. This would be equivalent to a “free radical protection factor” of 2, not the 15 to 50 SPF common for sunburn protection (Haywood 2003).

The balance may shift if people apply too little sunscreen or reapply infrequently. For example, a study found that for 3 common sunscreens the amount of free radicals caused by sunscreen exceeds the amount on untreated skin after 1 hour (Hanson 2006).

Particular sunscreen ingredients or formulations may be more damaging to skin than others. Both nano-size*zinc oxide and titanium dioxide, including forms extracted from sunscreen, react strongly with UV light (Dunford 1997) and may damage skin cells (Sharma 2009). Manufacturers typically use coatings that reduce activity (Popov 2009, Serpone 2006). Furthermore the crystal structure of titanium dioxide (anatase vs. rutile) also appears to affect its potency in free radical generation (Lu 2008).

The UV filter Padimate O causes skin damage through an entirely different mechanism. It fell out of industry’s favor when evidence emerged that it reacts with other compounds to form a mutagenic contaminant (Loeppky 1991) and causes a dramatic increase in DNA strand breaks relative to untreated skin (Gulson 1999).

It is difficult to gauge the effectiveness of a particular sunscreen formulation at combating free radicals**. Zastrow (2004) has proposed an Integrated Sun Protection index that would quantify the degree of free radical formation under UV light.

 *NoBurn and BikerButter Sunscreen were formulated with micro sized Zinc Oxide to provide a safe FDA approved alternative to these issues*

**Free radical protection may be found through the use of Beurre de Soleil after sun lotion**