Last Modified: May 6, 2007
Dear OncoLink "Ask The Experts,"
I have a question about sun block products. What active ingredients should be present in a product to be effective and in what percentage. Also are their any products that you can suggest. Brand names can be helpful.
Suzanne M. McGettigan, MSN, CRNP, AOCN, Board Certified Adult Nurse Practitioner and a Certified Oncology Advanced Practice Nurse, responds:
The sun produces two types of ultraviolet light that lead to skin damage, UVA and UVB. These rays cause redness, sunburns and, over time, can cause aging, wrinkling, freckles, and age spots. Sunburns are particularly dangerous for kids, as this is a strong risk factor for developing melanoma. There is no "safe" or "healthy" tan, and sunscreen is just one important step to protecting our skin.
The first step in preventing melanoma and non-melanoma skin cancers is truly sun avoidance, meaning that you should avoid sun exposure during peak hours, which are between 10am - 4pm. If you must be exposed to ultraviolet radiation or choose to do so, then you should seek shade and use sun protective behaviors. These include wearing long sleeve shirts, pants, a hat, and sun glasses. Clothing should have a tight yet breathable weave to be truly protective (a typical white t-shirt has an SPF of 3). There are products that you can wash clothing in to increase its SPF rating. Hats should have a wide brim. Sunglasses should protect against UVA and UVB rays. Sunscreen should also be worn.
It's important to think "outside of the box" about sun exposure and the need for protection. It is certainly possible to get sunburn on a cloudy day or being outside in the winter. We get a good amount of sun exposure riding in our cars on a sunny day, but we often don't think of this as a time when we need sun protection. The message is, make applying SPF (sun protective factor) a part of your daily routine, not something you only do when going to the beach.
At this point we know that sun exposure is linked to melanoma occurrence; however, it is less clear whether the link is between exposures to UVA or UVB rays. On-going studies are looking at this question, so for now we recommend protecting against both. There have been great increases in the numbers of melanoma cases, and experts question whether sunscreen use offers users a false sense of security against melanoma and non-melanoma skin cancers. So, while it is important to use SPF, it is also important to remember that this cannot prevent all sun damage. Our most effective tool to measure a product's ability to block harmful UV radiation is the SPF or sun protective factor. This number is tested in a laboratory to determine the ability of a product (typically clothing or sunscreen) to prevent erythema (redness) or sunburn in response to sun exposure. The SPF rating can be multiplied by the time of exposure necessary to produce minimal redness in an unprotected individual. For example, if you typically develop minimal redness after 20 minutes in the sun, using an SPF -15 sunscreen would extend the time to developing redness to about 300 minutes (5 hours) of exposure. It is important to note, that while SPF may correlate well with degree of protection against UVB, it does not ensure adequate protection against UVA, which is thought to play a key role in photo aging (aging of skin from sun exposure). One must also remember that water exposure and sweating can wash away the SPF and decrease the ability to protect your skin.
Sunscreens work by absorbing or reflecting and scattering the sun's rays. There are two main types of sunscreens, physical and chemical. When looking at a product in the store, look for the SPF factor and what ingredients it contains.
- Physical sunscreens contain large particulate substances such as titanium dioxide, zinc oxide, talc, kaolin, ferric chloride, ichthamnol (Ichthyol), and various colored clays, which act to reflect and scatter both visible and UV light. These sunscreens protect from UVA and UVB rays (called "broad spectrum sunscreens); however, they do exhibit qualities that users can find unappealing such as appearing white or colored, a tendency to stain clothing, and causing comedogenesis (obstructing of follicles leading to blackheads & acne).
- Chemical sunscreens absorb rather than reflect UV radiation, and they typically have a limited spectrum of protection. Substances that protect against UVB rays include Para-aminobenzoic acid (PABA), PABA esters, salicylates, camphor derivatives, and cinnamates are in this category. Newer products also protect against UVA rays; these substances include dibenzoylmethanes, anthranilates, benzophenones, triazoles, and some camphor derivatives.
Proper application of sunscreen is essential to achieving full benefit from any sunscreen product, regardless of SPF. Sunscreens should be applied evenly approximately 15 to 30 minutes before sun exposure and every 2 hours for it to work properly. Approximately 30-35 milliliters (about 2 tablespoons) of sunscreen is required to properly cover an average adult, but most people apply significantly less sunscreen than this. The American Academy of Dermatology recommends a sunscreen of SPF 15 or higher to be used in most circumstances; however, for individuals with greater sun sensitivity or in circumstances of prolonged sun exposure, higher SPF may be more appropriate. Reapplication of sunscreen should occur minimally every 2-3 hours, or after swimming and activities with sweating (even "waterproof" sunscreens must be reapplied!).
Self tanning lotions or sprays are a safe alternative to the sun, but remember that this does not give you protection, so you will still need to use SPF after tanning with these products. Tanning booths are not a safe alternative to the sun. They can cause skin cancers and promote aging, just as the natural sun can.