10 Tips: the ABCs of using sunscreens

Choosing the right sunscreen for your children is challenging. And applying it correctly (and repeatedly) is a hassle for you and annoying for them - but far less annoying than is a bad sunburn.

Here is what you should know:

1. Differences between chemical and physical sunscreens.

Chemical sunscreens are by far the most popular. They permit tanning and, if used correctly, prevent burning. Apply 30 minutes before sun exposure. This enables it to penetrate the skin and absorb harmful ultraviolet (UV) radiation.

Physical sunscreens or sun blocks shield the skin from the sun, reflecting more than 99% of harmful rays, and prevent tanning. Until recently only messy creams like zinc oxide were available. But now there are "micronized" substances that are virtually invisible. Sun blocks can be applied just before exposure. They are becoming increasingly popular.

2. Sun protection factor (SPF) numbers.

SPFs deal only with chemical sunscreens. The numbers are based on how long, not how well, a product protects skin from radiation. Example: A specific amount of sun-like radiation in a laboratory causes a measured amount of "sunburn" on unprotected skin in 10 minutes. A sunscreen is then applied to the skin. It now takes the same radiation 300 minutes to produce the identical amount of sunburn. The SPF number of that sunscreen is 30 (300 minutes divided by 10 minutes = 30.)

3. Shortcomings of SPF numbers.

Many sunscreen labels state their SPF to be 30, for example, or six hours of protection, yet may recommend reapplying every two hours. The reason: SPFs are determined indoors, under ideal conditions and with specific thickness. In practice, most people apply only one-half to two-thirds of the recommended thickness, halving its effectiveness. Protection is also affected by wind, humidity, perspiration, environmental temperature, and many other factors. A coat thicker than recommended increases protection very little.

4. SPFs of 30 suffice for everyday sun exposure.

They absorb about 97% of harmful rays. Sunscreens with higher SPF numbers may absorb slightly more radiation but contain additional substances that may increase the chances of skin reactions, itchiness and rashes, for example.

5. Applying the correct amount of sunscreen is surprisingly difficult - and expensive.

Cover all exposed skin with a thin layer. A one-year old child wearing a bathing suit requires about one-third of an ounce (10 cc) per application. A 7-year old, about two-thirds of an ounce (20 cc). Average-sized adults wearing skimpy bathing attire require one ounce (30 cc). Many sunscreens come in 5 ounce (150 cc) bottles, requiring one-fifth of the bottle for each application. Apply to lips, nose, an around ears, areas vulnerable to sun damage.

6. Familiarize yourself with one or two products.

Sunscreens are available as gels, liquids, sprays, foams, and solids (lip balms.) Additional ingredients (alcohol, for example) enhance the sunscreens’ ability to penetrate the skin and retard its removal by perspiration and immersion in water. For sensitive skin try out sunscreens on an area of skin the size of a hand. If itchiness or a rash develops, try a product with a different formulation. Some ingredients (vitamins, for example) are added to reduce skin damage, but there is little evidence that such additives are beneficial.

7. Travel and recreational activities may require specific products.

About 70% of UV radiation penetrates the top 12 inches of clear water, making swimmers’ backs vulnerable. Products labeled "water resistant" provide protection for about 40 minutes in the water, those labeled "waterproof", 80 minutes. For surfing, reapply every 30 minutes. Products labeled "sport sunscreens" are perspiration-resistant, and claim all day protection. Avoid oil-based products in hot climates and when engaging in strenuous activities; they may hinder perspiration, increasing risks of heat-related problems. Use water-based lotions or creams. White sand reflects most of the radiation that reaches it. Radiation increases about 4% for every 1,000 feet (300 meters) of elevation. Special products are available for each situation. Read labels. Check the web.

8. Apply sunscreens first, then insect repellents.

The repellent can be applied just before exposure. Insect repellents coat the skin. However, insect repellents may reduce the effectiveness of sunscreens by a third. Also, avoid sunscreens with fragrances when hiking or picnicking as they may attract bees.

9. Use milky lotions or cream sunscreens on young children.

These are more soothing than clear lotions, do not contain alcohol, and you can see where you applied it. Creams and lotion are also less drying than gels or alcohol-based products. Never use baby oil; it increases burning. Avoid applying sunscreens to the upper and lower eyelids as children tend to rub their eyes and sunscreens may irritate eyes. Protect eyes and lids with sunglasses instead.

10. Sunscreens may be used on infants less than 6 months of age, if essential.

Labels say no, because sunscreens have not been tested on this age group. But there are no known adverse effects Likely sunscreens are far safer than sun exposure; exposure for this age group is very detrimental. Infants should be kept out of the sun as much as possible. If sun exposure is totally unavoidable, most experts recommend sunscreens for exposed parts of the body.