Chapter 29: Sunscreens

INTRODUCTION

For several years, dermatologists have exhorted their patients to avoid or, at the very least, severely limit exposure to the sun since ultraviolet (UV) radiation is the primary cause of skin cancer, exogenous skin aging, wrinkles, and blotchy pigmentation.¹ In spite of these attempts to educate the public, the incidence of skin cancer is increasing at a disturbing rate. In 2005, there were an estimated 60,000 melanoma cases diagnosed in the US. Alarmingly, there are approximately 8000 deaths in the US related to this most potent and fatal of the skin cancers per year.² Cosmetic patients offer a captive and interested audience that can be educated about the hazards of the sun and the need for corresponding protective behavior. Of all the skin care advice that is doled out to patients, it is likely that this is the most important, because proper protection from the sun will make a great difference in the patient’s future appearance. Patients should be advised that if they do not avoid the sun and practice protective measures, they are wasting their money on cosmetic products and procedures.

Obviously, the daily use of sunscreen is an important adjunct to skin protective behavior. However, because no sunscreen can effectively block all parts of the UV spectrum, sun avoidance, protective clothing and hats, and window shields can all be utilized to lessen acute and cumulative sun exposure. Patients should be instructed about the proper use of sunscreen and asked about sunscreen use at every visit. This constant nagging will help them realize how important it is to protect their skin from the sun. Even if patients claim to use sunscreen and know about the hazards of the sun, studies have shown that they still do not get enough sun protection. In fact, it is known that mothers provide more sun protection to their children than to themselves,³ and that sun protection attitudes tend to subside from childhood to adolescence.⁴ Even well-intentioned sunscreen users can forget the rules. For example, one study found that 98% of 352 family groups applied their sunscreen after arrival at the beach, instead of 30 minutes before as is suggested for optimal sun protection.⁵ This chapter discusses the practical aspects of sunscreen formulations and selection, which should enhance the practitioner’s ability to help patients find the best sunscreen protection for their skin type and lifestyle as well as answer patients’ numerous product questions.

ULTRAVIOLET A AND B

On a typical summer day, UVA comprises about 96.5% of the UV radiation reaching earth, leaving UVB only with the remaining 3.5%.⁶ When compared with all kinds of light reaching the earth’s surface, UVA makes up 9.5% (Fig. 29-1). While UVA is the predominant UV light reaching the surface of the earth, UVB exposure is more likely to cause squamous cell carcinoma in an experimental setting.⁷ This supports ...