Reference 2 reviews some aspects of the use and misuse of sunscreens. Please print out this reference. It will answer many questions that your patients have of how and why to use sunscreens.
Sunscreens can be discussed in two broad categories. The opaque sunscreens are sunscreens that do not permit light to penetrate the skin. Zinc oxide or titanium dioxide, applied thickly, are in this category. The major advantage of an opaque sunscreen is that it provides a complete block by reflecting ultraviolet light. It is of particular use at times of maximal exposure such as mountain climbing, competition sailing or other such activities.
Transparent sunscreens, on the other hand, are not risk free. Transparency is important from the cosmetic point of view. Few people can or will use a physical blocker in urban areas. However, with the transparency comes some ultraviolet light induced damage. It is not possible to block all ultraviolet light in a transparent sunscreen.
It is naïve to think that sunscreens do not change behaviour. It has been well documented that high SPF sunscreens are associated with increased time in the sun. This is both a benefit and a deficit. Clearly people would like to spend more time doing what they enjoy doing. High SPF sunscreens can permit this. The down side is that there can be a build up of low-grade damage caused by the transparency of that sunscreen. For that reason it is very important, when using a high SPF sunscreen, to use one that provides a very broad block. It is important to block UVA, in addition to UVB.
UVB blocking is the traditional sunscreen block. Many ingredients, added together, can block burning, which is the patient's major concern. Pure UVA, i.e. above 340 nanometers and below 400 nanometers, the cause of UVA sagging and possibly immune suppression, is blocked well by only one ingredient found in transparent sunscreens, Parsol 1789 (dibenzoylmethane). Very few dermatologists would recommend a sunscreen that did not contain this ingredient.
Sun avoidance may obviate the need for chemical sunscreen. Sun avoidance means reducing, whenever possible, activities between 11 am and 3 pm.
Clothing is an important sunscreen. Clothing is chemical free, and is inexpensive. Good clothing is a complete block. An important part of clothing is the use of a hat with a wide brim. This at least provides partial screening for the face. A 7 cm brim is an SPF 20 on the forehead, but only 4 to 8 to the nose. Hats alone are not enough. There are UV blocking clothes on the market which have a specific weave that permits airflow, while blocking ultraviolet light. These clothes tend to be expensive, but they are generally effective.
Glass is an excellent sunscreen for preventing burning. You will not burn through window glass but you will tan through window glass. Theoretically you can wrinkle through window glass.
Tanning salons can be a significant cause of UV damage. Most tanning salons now use UVA tubes rather than UVB tubes. This is a step forward. However, the UVA tubes do emit a small amount of UVB, probably in the order of 1% to 2% of total energy produced. As exposure times are quite long in the UVA light beds, this can be a significant exposure to UVB. UVA alone is only a small contributor to skin cancer risk, but is an important cause of skin sagging.
The use of tanning beds is promoted for colour, and protection. The bronzing creams containing dihydroxyacetone can give a brown colour, at very low risk, should that be desired. The argument for inducing a tan so that there will be fewer sunburns is less easily dealt with. Clearly a suntan does provide some protection; it has been suggested that a dark suntan equals a SPF 4 sunscreen. Equally certain is that the suntan was the direct result of skin injury by the ultraviolet light. A better approach would be to avoid the tanning parlor, and use a high SPF sunscreen at the beach.