Summer is finally here and as the sundresses, shorts and sandals emerge from the back of the closet, its important to remember to ward off sun damage to your skin by using a high-quality sunblock or suncreen that protects against ultraviolet (UV) rays. Sunlight contains three types of UV rays - UVA, UVB and UVC. Fortunately, the ozone layer blocks out the most dangerous UVC rays and some of the UVB rats.  Long-wave UVA rays pass through the ozone layer unfiltered, deeply penetrate the skin and are known to cause photoaging and wrinkling.  Short-wave UVB rays cause sunburn and are implicated in basal cell and squamous cell carcinomas.

UV radiation can be blocked by chemical or mechanical sublocks. Chemical sunblocks are typically synthetic compounds which work by absorbing the UV light.  They are absorbed into the skin and often into the systemic circulation.  They can be degraded by the UV light and and can take up to 20 minutes after application to the skin to reach effectiveness.  Therefore, it is important to apply a chemical suncreen before sun exposure and then again at regular intervals during.  Some chemical sunblock ingredients include dixoybenzone, oxybenzone, PABA and PABA esters and cinnamates. 

Mechanical sunblocks reflect and scatter UVA/UVB light.  These sunscreens typically contain titaniun dioxide and zinc oxide as active ingredients.  I prefer mechanical sunblocks as they begin to work immediately after application and systemic absorption tends not to be a problem.  In the past, these preparations were thicker, opaque, and somewhat  cosmetically unacceptable (think the white blob of sunblock on a lifeguard's nose). With currently available technology such as micronization, the titanium and iron particles have been processed to be much smaller resulting in translucent suspensions that are thinner and smoother than in the past. 

As far as the Sun Protection Factor (SPF), you should aim to use a suncreen with at least an SPF of 30. Chemical sunblocks typically do not provide additional protection beyond SPF 30.  Mechanical sunblocks are usually by their very composition at least SPF 45-50, so you by choosing a mechanical sunblock, you are automatically at what I consider to be the a maximally efficacious level.  In either case, frequent reapplication is of the chosen sunblock is key to skin protection. Additionally, don't forget to employ some other common sense tactics such as wearing a wide brimmed,sunglasses and protective clothing, as well as avoiding the sun during the hours of 10am and 2pm to maximize your skin's protection.