Understanding SPF or the Sun Protection Factor

The term SPF stands for Sun Protection Factor and is supposed to indicate to us how much of protection we get from the harmful rays of the sun when we are out in the sun.

We are often urged by skin care magazines and experts that we must slather on a lotion with “at least 15% SPF” before we go out into the sun. The sun screen works by absorbing the ultraviolet radiation of the sun which is harmful for the skin. Many sun screens, creams, lotions and gels on the market have a very high SPF count and may also be more expensive.

This leads many of us may believe that the higher the SPF the better protected our skin is. Yet is this the case? Does the skin protection increase in proportion to the SPF number on the tube? If a sunscreen of SPF 15 lets you stay out in the sun for 2 hours, will an SPF 60 sun screen let you remain in the sun for 8 hours; which is the proportionate increase?

Well not exactly. It isn’t that simple.

How does SPF work?

Having a higher SPF doesn’t mean that there is a proportional increase in the absorption of UV rays or that there is a proportionate increase in the number of hours you can stay out in the sun. If a person gets sunburned after 10 minutes of unprotected exposure to the sun, it doesn’t mean that he or she can stay out in the sun for 12 hours if they have on a sun screen of SPF 70.

In fact according to the How Stuff Works website, an SPF of 2 means that about 50% of UV radiation is absorbed; at 4SPF about 70% is absorbed. At SPF 15 about 93% is absorbed; but at exactly double that SPF; at SPF 30%, that protection doesn’t (and obviously cannot double). It rises only to 96.7%; a fractional increase of about 3.3% only!

Skin protection depends upon more than just SPF

The skin type of the user is a determinant: dry skin or oily; light or dark skin; the ability of the skin to absorb the sun screen all impact how well the sunscreen will work.

How much of the product is applied on the skin is probably as important if not more important than the SPF. The frequency of application is another important determinant.

The level of activity post application is important: swimming and sweating will reduce efficacy even or the so called “waterproof” sunscreens.

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