People often say, “Jim you’re ugly.  You should have worn more sunscreen when you were young.”  I have to admit, I generally didn’t back in the day.  Now I am more sensible.

    I have always found the SPF factors rather confusing.  Obviously, higher is better.  But what exactly does the SPF number mean?  I did what any person might do now –a-days.  I Googled it.

    Here is information extracted from several website related to Dermatology.  The information has been checked against a couple of medical web sites I know of, so I think it to be reliable.

    What is SPF?

    SPF stands for Sun Protection Factor.  The number is determined experimentally indoors by exposing human subjects to a light spectrum meant to mimic noontime sun. Some subjects wear sunscreen and others do not. The amount of light that induces redness in sunscreen-protected skin, divided by the amount of light that induces redness in unprotected skin is the SPF. It is mainly a measure of UVB protection and ranges from 1 to 45 or above.

   The ingredients in sunscreen protect the skin by either absorbing or blocking and scattering UV radiation.  Sunscreens are rated by the Sun Protection Factor (SPF) system. The SPF rating is primarily the amount of UVB protection the sunscreen provides.  The rating (SPF15, SPF20, etc.) indicates how much longer a person can be in the Sun before burning than when not wearing sunscreen.

   For example:

   Suppose you can stay in the Sun for 10 minutes before starting to burn if you are NOT wearing sunscreen. When using sunscreen you can stay in the Sun your initial 10 minutes multiplied by the SPF rating. So if you use a sunscreen rated SPF15, you should be able to stay in the Sun for 150 minutes (10 x 15) or 2.5 hours before starting to burn. Reapplying sunscreen reinforces the protection although it does not extend the time you can remain in the Sun.

    The "protectiveness" of clothing can also be measured by SPF. The following are SPF's of various types of clothing:

Nylon Stockings - SPF 2
Hats - SPF 3-6
Summer-weight clothing - SPF 6.5
Sun-protective clothing - up to SPF 30

    How to choose a sunscreen?

    [These guidelines were also listed in one of the websites.]

    The best sunscreen is one that blocks enough UV radiation to protect your skin. The chart below can be used as a guideline to obtain the proper protection.

    REMEMBER:  You should always consult with your physician when choosing the proper sunscreen ESPECIALLY if you are taking any medications that could result in photosensitivity.

    Type I - Very fair; unexposed skin is white; blue eyes, freckles.  Tans little or not at all; always develops a painful burn quickly.
SPF 30 - 50

    Type II - Fair; red, blonde, light brown hair; unexposed skin is white.  Tans lightly and peels; usually develops a painful burn quickly.
SPF 30 - 50

    Type III - Average Caucasian; unexposed skin is white.  Develops an average tan; moderately burns.
SPF 15 - 20

    Type IV - Medium complexion; unexposed skin is white or light brown; usually with dark hair and dark eyes.  Tans easily and burns minimally.
SPF 6 - 15

    Type V - Dark, unexposed skin is brown.  Tans easily and substantially; rarely burns. SPF 2 - 10

    Type VI - Very dark, unexposed skin is black.  Becomes deeply pigmented and never burns.
SPF 2 - 10