With hundreds of available choices, confusing labels, and misleading SPF numbers, it’s no wonder that patients always have questions about sunscreens. We know that exposure to UVA and UVB ultraviolet light accounts for 90% of premature skin aging: wrinkles, hyperpigmentation and skin cancers. The hands-down, number-one skin-care product to prevent wrinkles and skin cancer is sunscreen, but most people do not use this product correctly.
Factors to consider with sunscreen use are: the UV radiation spectrum, the amount of sunscreen applied, and the frequency of application.
The sun gives off ultraviolet (UV) radiation that can be divided into categories according to wavelength. The shortest rays, UVC, are absorbed by the atmosphere and don't really impact our skin. UVB radiation affects the outer layer of skin, the epidermis, and is the primary agent responsible for sunburns. UVB does not penetrate glass, and the intensity of UVB radiation depends on the time of day and the season with Summer and high noon being the most intense. UVA rays are longer wavelengths; these penetrate deeper into the skin and cause collagen breakdown(aging). The intensity of UVA radiation is more constant than UVB without daily and seasonal variations. Unlike UVB, UVA is not filtered by glass. Since UVA is prevalent on cloudy days and all seasons everyday, this is the reason we Dermatologists preach daily sunscreen use.
There are two types of sunscreens: physical blocks, which physically block the sun’s rays, and chemical blocks which absorb radiation. The physical blocks protect against the full spectrum of the sun's harmful rays, and these sunscreens don't degrade over time (although they can get rubbed-off). Newer formulas containing micronized zinc oxide and titanium dioxide are much less opaque than the zinc blocks of the past and are cosmetically acceptable for everyday use.
Chemical Sunscreen ingredients are differentiated by the type of radiation they absorb - UVA absorbers and UVB absorbers. The SPF (sun protection factor) measures the amount of UVB absorption, but there is currently no universally-accepted method of measuring UVA protection. The best sunscreens combine some chemical and physical block ingredients.
Most people do not apply nearly enough product for the sunscreen to be truly effective. It is a common complaint of my patients to proclaim that they still got sun despite applying sunscreen. Why? ...because they are not reapplying! Sunscreen should be applied liberally enough to all sun-exposed areas so that it forms a film when initially applied. It takes 20-30 minutes for sunscreen to be absorbed by the skin, so it should be applied at least a half an hour before going out in the sun. Re-applying sunscreen every two hours is also critical to ensure adequate protection. Sunscreen should also be reapplied after swimming, excessive sweating, or toweling. Please put on your sunscreen every morning and reapply before spending time outdoors. The daily use of a low-SPF sunscreen (15) has been shown to be more effective in preventing skin damage than the intermittent use of a higher SPF sunscreen.
Of course, proper use of sunscreen is only part of a sun safety plan. We tell our patients to remember their wide-brimmed hats, minimize mid-day exposure between the hours of 10 am and 2 pm, and wear 100% UV-protective sunglasses whenever possible.
Dr. Susan Ellis, MD, is a Morristown based Board-Certified Dermatologist specializing in Cosmetic and Surgical Dermatology. Her expertise includes Laser Treatments, Injectable Fillers, Botox, Sclerotherapy, and scar revision surgery. She is on the Board at Morristown Memorial Hospital, and speaks regularly on cosmetic and general dermatology.