By Mark E. Burnett and Steven Q. Wang
Photodermatology, Photoimmunology & Photomedicine Volume 27, Issue 2, pages 58–67, April 2011
Until very recently, most humans spent most of their waking hours outdoors exposed to sunshine. In the past few centuries, life for many people has moved indoors, drastically reducing exposure to sunlight. In the past few decades, people have started using creams containing chemical sunscreens to prevent sunburn, wrinkles, and cancer. Concern has been aroused that these novel aspects of the modern environment may cause estrogenic stimulation, vitamin D deficiency, and possibly even skin cancer. The above comprehensive review by Burnett and Wang summarizes the current state of the evidence..
They conclude that sunscreen use:
- Does not influence the risk of melanoma,
- Probably does not decrease the risk of basal cell carcinoma,
- Definitely decreases the risk of squamous cell carcinoma,
- Probably does not decrease sun exposure enough to cause vitamin D deficiency in routine use, although whole body application completely blocks vitamin D synthesis.
The article also summarizes evidence on effects of components of sunscreens:
- Oxybenzone, a major component of most sunscreens, has definite estrogenic effects in vitro, and is absorbed through skin, however it is excreted in the urine and sunscreen users shown no hormonal differences from controls.
- Retinyl palmitate generates free radicals on exposure to UVA radiation, but there is no evidence that topical use prevent skin cancer, and there is good evidence that oral use and prevent skin cancer in special populations, such as those with xeroderma pigmentosum.
- Nanoparticles of TiO2 and ZnO do not penetrate deeper layers of normal skin, but their safety for damaged skin has not been shown, and UV induced chromosomal damage was greater in in vitro studies of cells exposed to nanoparticles.
The authors appropriately emphasize that most of the relevant studies were conducted using antiquated sunscreen formulations, and that the evidence on most of the above point is inadequate to draw firm conclusions. They state no conflicts of interest, but do not provide information on sources of funding for their work or the studies they cite.