It is important to understand some basic principles behind sun exposure and ultraviolet radiation in order to understand what the various sunscreens on the market have to offer.
The sun's ultraviolet rays are measured over a spectrum of different wavelengths. Only some of the ultraviolet rays are harmful, namely those between 290 and 400 nanometers. Some of these rays are called
UVB rays (290 to 320 nanometers) and some of these rays are called
UVA rays (320 to 400 nanometers). The UVB rays are the rays responsible for a sunburn and they are partly responsible for skin cancers. The UVA rays don't cause a sunburn like the UVB rays, but the UVA rays penetrate deeper to damage the skin, leading to wrinkles, brown spots and other indicators of cellular damage. The UVA rays also cause skin cancers.
Many of my patients proudly say to me, "I wear an SPF 50 sunscreen." When I ask them what the ingredients are, 99% don't know. Unfortunately, SPF only refers to the UVB rays. 100% of the UVA rays could be going right through the sunscreen to damage the skin and cause skin cancers, even though one is wearing an SPF 50. Furthermore, the UVA rays penetrate glass and they are just as strong in the morning and afternoon as they are at noon. Luckily, most sunscreens today offer both UVA and UVB protection, but the amount of protection varies from sunscreen to sunscreen.
The best ingredients, in my opinion, are
zinc oxide and
titanium dioxide, since these substances block almost all of the harmful UV rays. Zinc oxide and titanium dioxide are known as
sunblocks, not sunscreens, since they physically block the UV rays. Most other sunscreen ingredients react chemically with the UV rays, as opposed to physically blocking the rays. Therefore, these are called
sunscreens.
A sunscreen that has been touted as one of the best for blocking UVA rays is
avobenzone (
Parsol 1789). However, it is not commonly known by the public that Parsol 1789 breaks down when it is struck by UV rays. Therefore, although Parsol 1789 is an excellent UVA sunscreen, it must be reapplied frequently throughout the day.
Something people always forget is the amount of reflective UV exposure that people get. Everyone realizes that water and snow reflect, but what about sand, concrete and grass?
Finally, many people think that wearing clothing is a fool-proof sunblock. However, anyone who went swimming as a child wearing a T-shirt to prevent sunburn knows that a wet T-shirt is about an SPF 1 or 2. The same applies to thin, gauzy material. Although these materials are cooler, a tightly woven fabric provides far more UV protection.
